And where do these trace it to? Dungeons and Dragons. The original published version of D&D had six classes - the Fighting-Man, Magic-User, Cleric, Elf, Dwarf, and Hobbit.
- Fighting-Man was basically the Fighter/Warrior as we know it today, but with fewer mechanically-enforced options
Magic-User was a wizard with extremely limited spell slots, especially at low levels
Cleric was primarily there as a mechanical hard-counter to undead enemies, who could not be bribed or intimidated and were difficult to sneak around; they don't even get spells until after leveling up as a fighter with Turn Undead. Think less "white mage" and more "paladin".
Elf was just a wizard who could decide every day to be a fighter instead if he felt like it
Dwarf and Hobbit were just Fighting-Man with an unfavorable level cap, the dwarf getting a few non-combat utility abilities and the Hobbit getting excellent combat mobility
- Fighter - Your main go-to guy when it comes to killing mortal foes from men to beasts to goblinoids to giants.
Wizard - Able to accomplish many amazing, fantastical feats but can only do a few such things a day and needs to prepare in advance and hope he made the right selections for the challenges he'd face that day
Cleric - Barely less able in melee than a Fighter, but also able to drive away evil spirits and zombies and able to heal injuries, something even the greatest arcane wizard would struggle with.
Thief - Slightly less able in melee than a Cleric but still better than a Wizard, the Thief's main usefulness lay not in combat skills but in non-combat utility; better at climbing, sneaking, listening, hiding, and able to spot and disable traps and pick locks. The thief helped you get better value out of all the treasure your party found while the other three helped the thief survive to get to the treasure in the first place!
For Dragon Warrior type games, a standard balanced four-man party is:
- A jack of all trades type hero, usually slightly stronger in the combat and white magic fields, then black magic third. He'll be the second-best tank, second-best physical attacker, second-best healer, and second- or third-best black mage.
A warrior with no or extremely limited magic power, but undeniably the best in physical combat. Best tank, best physical attacker, magic use N/A.
A black mage, casts spells that do damage and spells that buff or debuff, but probably forbidden from healing unless it's an HP-draining attack spell.
A white mage, probably slightly stronger physically than the black mage and the best healer, probably also has buff and debuff spells. Might be better or worse than the jack of all trades hero at attacking with magic.
But you know one thing I don't think most games need? More than four heroes in a total adventuring party. More than four hero definitions maybe, for customization or class changes; Final Fantasy 1 had six hero definitions and a four-man party so you could use a fighter, thief, red mage, and black mage (or my usual preferences, fighter/black belt/red mage/white mage or fighter/fighter/red mage/white mage). Dragon Warrior 3 had a single required hero, 4/5* non-magic fighters with varying levels of combat and non-combat utility (Warrior, Fighter, Jester, Merchant, and in the remake Thief*), Cleric, Wizard, and a special Cleric-Wizard who could only be gained by [spoiler]leveling up the disobedient goof-off Jester to level 20 or using a rare consumable item at a certain mid-game location[/spoiler]. You can define any number of them you want and leave them at the tavern, but you can only have three in a party at a time.
When you allow a player to swap in and out heroes beyond a maximum of four, things start getting weird. Only swapping at a designated base of operations of some sort where non-active heroes stand around or perform some sort of function when not in your party? Okay, I can kinda get it, but it doesn't explain why you only have four guys active when there's a total of five.
When you've got like ten, or a dozen, or 106 heroes it makes all sorts of sense on multiple levels to keep active group sizes down from both an in-universe perspective for certain types of quests and a game mechanical one. But if the story is only written such that five heroes are actually significant, why not just let five rather than four form a single active combat party? That's how many heroes you usually have in a sentai/power rangers team and it has many balance options of its own.
When you go to an inn and only active party members are healed, none of the reserves; did all those other guys simply not sleep because the player wasn't watching them?
And then allowing hero swapping anywhere is another can of worms entirely. Game mechanically it means you can remove danger from certain characters simply by putting them in your bag of holding - monsters and harmtiles won't hurt them, and maybe you have filler characters in there to provide a little extra tanking and damage while you wait to go to the inn to heal the character you actually care about. Storytelling-wise, how is a party of 20 or 30 heroes navigating all over the place, but monsters are politely only ever attacking the four in front and nobody in the back rows, spread attacks like Tornado and Nuclear Explosion are only hitting the four in front, and so forth? And worst of all, how is it a game over if those four in front die when there's a dozen other heroes at the player's beck and call to pull out of storage mid-dungeon...why not mid-fight?
The only game I've ever personally seen pull that off well was Dragon Warrior 4 (and I hear Golden Sun 2 had the same answer once you united with the party of Golden Sun 1, which had five total playable heroes but only four in the total party ever). This solution being that on the overworld your front four heroes participate in random battles but the four in the wagon will jump out and take over if their allies fall; in a dungeon, your four reserve heroes wait outside since the wagon is too big and bulky to take up and down staircases, so all four dying means death. (The usual generous Dragon Warrior party wipe: You're teleported back to the last place you saved, your money is cut in half but you keep your experience and items found.)
The best answer for most seems to be "Don't worry about it, it's just a game mechanic. All these heroes are necessary for game mechanical/storytelling reasons." But are they, really? Is it actually necessary game mechanically to have eight heavily armored warriors who each wield exactly one type of weapon, wear the same armor, and have exactly one combat technique...possibly not even unique? To have one thief who pickpockets and uses time magic and another who throws weapons and uses direct damage magic? Why not consolidate those two archetypes down to two heroes, each with a solid array of options? Do you need an Alchemist and a Black Mage to be separate characters? Or for that matter, do you really need to divide the mage role into a healer and a damage dealer instead of just having mages learn healing spells? No matter how many game mechanics you have in mind for combat, I'm absolutely certain you can fit it on a four hero party if you want to, and this will reduce the need for redundancy like "make sure every character can heal in some way" and such.
And when it comes to storytelling, a lot can be said for having more than four important good guys. It makes all sorts of sense that a bunch of people see saving the world or overthrowing a specific tyrant as an important deal, and maybe a few of them are able-bodied enough and free of other obligations to be able to join an adventuring party. This is when it's best to contrive reasons for the group to split up, to be divided into four-man bands for a split attack on the main enemy or whatever. Or have beloved heroes actually story-die at crucial moments making convenient free slots, so long as the new guy is actually different and not just a cheap clone of the other guy (like maybe your main warrior dies and is replaced not with another physical attacker, but a new mage). But maybe you can't contrive any more reasons to keep the party size at 4 or fewer heroes available to the player; the storytelling reasons for allowing more heroes will, to most, take priority over the verisimilitude reasons to forbid hero swapping and weird arbitrary party size limitations.
But here's another thing about having all those heroes: It's really hard to balance that many important characters getting the spotlight. It's hard balancing four or five, quite often people just resort to either the first guy in the party (a warrior or jack of all trades type) or the main girl who is probably his love interest for little or no reason (most likely a white mage) to be "The Chosen One" and more plot important than all the other heroes. I'll use an OHR game I love as an example here: Walthros. It's about as ancient now as the NES classic RPGs were when it was made so I feel it's a classic game worth examining here; it's definitely written well enough to be one. But the character roster:
- Bob is absolutely necessary (both as the main character and as the main healer, wonderful double duty there and I loved the main character being something other than a generic skirmisher type)
Salom is a great second man for Bob to bounce off of. His personality may not be at all consistent from game to game, but it is pretty consistently strong no matter what form it takes.
Super Walrus Man could have been written out of the plot for the most part, but he was loads of fun to read and play so his existence is justified
Yuk Deluxe was superfluous and entirely optional; mostly his existence shows how nefarious it is to genetically engineer living creatures and sell them as combat slaves.
Dinosaur Triple; they're a fun trio in their own right, but asking three whole heroes to be added to the roster of an RPG already struggling to justify all the heroes it has is a tall order. Dinosaur Micro has an absolutely microscopic screen presence to the point that I can't remember a single line he's uttered in the whole series, Dinosaur Giant is both hilarious and very strong, and Dinosaur Super being a bit of a bossy jerk gets Dinosaur Giant and Rice some chance for character development down the line; was Dinosaur Super being playable necessary to have him hang around and be a bossy jerk though?
Woo is funny, but she's not really good in terms of gameplay and could basically have just as casually been written to stay in her home dimension or follow Super Walrus Man to the portal, pretend to join the party complete with fanfare, and then run away giggling at the last second.
Gulob is important only in outside information the players of the game weren't privy to (the Sky Flyers comics) and comes quite late in the game. He basically has no personality, no presence, and no game mechanical reason for the player to keep him in the active party. He could've been too busy rebuilding his kingdom after an attack or simply not able or willing to leave and not much would really change aside from the iconic "Sky Flyers" trio not coming together in this specific game (which they got in Gato Suico: The Quest For Color...where he's still basically a non-character again anyway).
Scotty is just Bob without magic or a personality. Barely improved sword skill, no personality, no story or gameplay reason to want to keep him.
The five Rodentian Mice...storytelling wise it's important within this chapter for them all to exist, have their own stories and adventures, but of these only two have interesting stories: Ketchup with the resistance against a totalitarian government and Rice with her quest to get a magic sword...and despite being a swordmaster as well as an archaeologist, cannot wield it herself, and gives character development to the gameplay and humor beloved Dinosaur Giant. Gameplay wise, Rice as a decent warrior and Blueberry as a versatile but thematic mage are the only ones worth keeping beyond this chapter aside from the one secret cave with a boss whom Ketchup easily defeats but other characters basically can't hit.
Dr. Pescado is there so briefly, and his skill set is just a pharmacy worth of healing items, not really much reason for him to be playable rather than just accompanying the party to the next major location as an NPC.
Sombra and the Guinea Cow are just to make Bob less lonely when he's on the moon. Sombra is useful and fun in combat.
I really doubt Walthros could've worked with only four playable heroes, so while some characters were basically filler it's all forgivable as a fantastic learning experience and will make a good example of pitfalls to avoid for future developers. I have very high hopes for the remake, which seems to be adding new characters I've never seen before and removing some of my old favorites; with that much changed, it'll be an entirely new experience!
Did Vikings of Midgard need both Kitt and Olaf, rather than having the young Viking warrior learn how to go berserk from the old man he admires? Did it need all three of Styrge, Bram, and Freki as separate characters, or Renard to be separate from Night? Probably not, but in this case it's only ten total heroes and they're all lovable in their own way (except I haven't seen Renard yet and I never once liked Bram). The game could've been done with only four heroes, but since the original version was based around showing off a simpler version of the character select from FFH and its 24 class/race combinations, starting with eight and turning the cursor herself into a full-fledged playable character later seems just fine.
OHRodents was of course an absolutely tiny game with a huge cast of near-disposable rodent heroes. Radar, The Grand Zark, Pikahcu, and Nathan are simply not as good of party members as Blueberry, Misa, Bob, Rice, Jude, or Ketchup but all characters receive very close to the same minimal amount of character development ("one amusing dialog exchange near the time they're added to the party and one drawing in the ending scene" with Nathan and Jude getting a little more because I could always count on them to be there). It was a joke game made for the Ridiculous Games Contest anyway so going over the top with this aspect of RPG rosters wasn't out of place.
But on the other end, I very clearly remember the four generic, nameless heroes of the original Spellshard demo. I remember their appearances, their strengths and weaknesses, their equipment lists, one of the wizard's spells being "discomb" in all lowercase instead of a four-letter word in all caps, and so on. From Okedoke I remember El Garbanzo the bandito in search of his father, Senor Death the reaper, Senor Rialgo the farting bullet-resistant martial artist, and Schnee the mage with large tracts of land. For a non-OHR game example, simplistic as they were, I remember the four heroes of the first Golden Sun game and their one personality trait apiece (Isaac = quiet but shoved into a leadership position; Garet = impulsive but well-meaning; Mia = compassionate but sensitive; Ivan = socially awkward and was never taught reading minds is rude).
I'm sure some people remember some of the set parties I've handed out in fours before; I usually don't feel like my project's really gotten off the ground until I have four heroes to work into the eventual party, and have of late become ever more fond of just giving the player all four from the start, worrying about character development later. I'd say I did a pretty good job of that with Trytuges; its main failings are first and foremost the lack of exploration rewards, and second being a little bit of problems with combat (which can mostly be fixed by dropping spell prices a touch, adding more accuracy to a couple of characters, and triple-checking the monster spawning elemental issues).
In Maces Wild, Ken was obviously thought of first; Hera was actually the second because I figured a coyote and a hare would make an interesting pair of characters and I could build him mostly out of right and 45 degree angles and her mostly out of circles. TOBMAC was added because I figured it'd be cool to have an in-universe explanation for the game camera to some extent/hero cops collecting video evidence, so I made a CAMERA ROBOT. I decided it could have a tiny, ineffectual gun turret arm that doesn't hit as hard as the main heroes, but started out super-durable and had its stats go down every level as machines wear down instead of building muscle. Ken and TOBMAC having a character dynamic was basically an act of pure impulse that I did not make consciously and if anything, I'd say it was some of the character writing in Village People: The RPG rubbing off on me (I would be a horrible liar to deny its inspiring me and greatly influencing Maces Wild). Lesley was me deciding to import a sprite from an abandoned 8-bit project I never got off the ground; I decided to explain his medieval attire and larger size by having him be in basically a frozen cave man situation, only for the Renaissance era (or maybe more recently, given his Elizabethan English).
In conclusion: I think more than four heroes is usually not needed, sometimes it is needed for the storytelling if you want to tell that kind of story, gameplay-wise it's probably unnecessary, and allowing hero swapping does weird things you need to just be okay with allowing.