MM1:
Leader = GutsMan
This should be obvious, for the numerous times he's appeared, revised as a Fortress boss. Plus, he's the big scary one, and the first gaming character ever equipped with a "seismic attack."
2nd in Command = ElecMan
He powers the team, quite literally.
Ironically, CutMan's "contribution" to the team (as a lumberjack) fits quite well with WoodMan's creation in MM2, don't you think?
MM2:
QuickMan = At first the leader, but he's too stubborn and independent to request help, or really, request ANYTHING from the other masters. Thus, a BAD LEADER. He turns rogue, and is later replaced.
Leader = BubbleMan
Something about Bubbles just screams "leadership." He's not out-of-control, and very deliberate-seeming in his actions, which are pretty planned out; as opposed to how reflexive/spontaneous many of the other Robot Masters are. Probably promoted from 2nd in command/strategist.
2nd in command = WoodMan
For crying out loud, 2 Leaf Shields are all it takes to do Rock in! He's clearly the powerhouse of the bunch; again, quite the irony for a robot made of wood. (See, CutMan is way sharper than you think he is! He's just not a good fighter.)
MM3:
Leader = ShadowMan
I'll give you that. Shadow seems like a very focused and confident leader.
2nd in command = GeminiMan
This is actually a pretty hard one, I'd almost give it a toss-up between GeminiMan and MagnetMan. Gemini might barely edge Mag out, though. He's clearly got the hardest, most impenetrable stage of the bunch. I think it's the only one that actually gets EASIER as a Doc Robot stage! He's also the quickest mover of the bunch, and for having such a basic attack pattern, it's pretty hard to avoid, entirely! (Imagine if, during the pause-shoot, the airborne one shot as well - seamless!)
MM4:
Leader = PharaohMan
Come on, with a name that reflects royalty, this much should be obvious! But like many ancient rulers, he relies too much on his followers (namely, the high-profile SkullMan and RingMan), is often lost in thought, and becomes somewhat lazy and overzealous as a result.
2nd in Command = SkullMan
Just as mummies and the undead are often a focal point of Egyptian Ruins, it should be no surprise that SkullMan would be favored in this position. His high mobility and defensive tactics make him rather formidable, and his heavy involvement (as opposed to PharaohMan's) probably warrants him as the most respected as well. Hence why he is often the "go-to guy" of the bunch, and easily mistaken as the actual leader.
ToadMan, I believe, is mostly for the entertainment of the rest of the crew. His attacks include crotch-rockets, and a damage-inducing hula dance.
How can that be for anything *besides* amusement?
MM5:
Leader = GyroMan
He's clearly the most assertive, offensive, and tactical of the MM5 masters; and his weapon, the Gyro Attack, is certainly the key to stage mastery. It matches the Napalm Bomb in offensive power, and it's just a blade!
2nd in command = GravityMan
Naturally, the only one of the Robot Masters in MM5 who could possibly keep GyroMan "in check," especially since most of the others' abilities are very ground-focused, and limited as such (Charge Attack? Water Wave? Napalm Bomb? Even StoneMan's tactics are very gravity-based).
MM6:
Again, each of the Robot Masters in this appear to work competitively and independently, rather than in cooperation. Hence why they're so easily conquered, there's NO solidity amongst any of them, at all!
MM7:
Leader = ShadeMan
Let's face it, 80% of MM7's "plot" revolves around this stage. Shades also takes the LONGEST to fight, and is very good at controlling the pace of things. He's sinister, yes; but VERY strategic.
2nd in command = FreezeMan
A tactical genius who's both the second strongest, AND the second quickest. Obviously the leader among the "first wave" of masters. These two could almost be interchangable.
MMV:
Leader = Terra
He takes... pretty much the entire initaitive in MMV. It's still unclear what he's got against Rock, unless he's really a Wilybot. SunStar -is- the big, overpowered boss, sure; but much like PharaohMan, will only get his hands dirty when he has to. And no doubt, SunStar answers to Terra, and not the other way around.
2nd in command = Jupiter or Saturn
I would side slightly with Jupiter here, can't quite explain why. There's just something about him, I suppose. Seems very defensive-minded and highly mobile; which is plagued by the fact that he's only equipped with short-range weaponry.
Saturn would be a *very* close second here, and it's not hard to imagine why. He pretty much takes what makes GeminiMan and MagnetMan formidable, and works with an odd combination of it.
MM8:
Leader = TenguMan
He's very direct, if a bit obnoxiously so. He's the perfect mascot to lead the charge - it's just so sad that his butt's usually the first one to get kicked because of it. Plus, the reason he leads, rather than SwordMan, is that many of the other, "energetic" Robot Masters take to his "go-get-em" attitude, instead of SwordMan's more patient one.
2nd in command = SwordMan
A bit slow to conflict, SwordMan's nobility is definitely leadership-worthy. If only the rest of the MM8 crew weren't a bunch of bolt-thirsty fiends, like FrostMan and GrenadeMan, or hyperactive kids like ClownMan and AquaMan. At least AstroMan still relates to him...
MM&B:
Leader = DynamoMan
He's the most heavily guarded Master of the bunch, with the screen-killing power; and also takes the most damage to kill. As a result, he's also most often the last one faced. His personality, to me at least, comes off as very "directorial." MM&B's team, for the most part; is probably the most solid of one I've seen since MM3, in fact. Bringing AstroMan in as a "personal bodyguard" appears to be his idea.
2nd in command = GroundMan
The "field leader," GroundMan appears to be the toughest and most direct of the bunch. He's also one of the quickest and smartest of the bunch; appearing to think both in terms of direct and indirect tactics. It's such a shame that his Spread Drill missile is the first of it's kind to NOT be used for block-breaking or passage-digging. I would expect that TenguMan's presence is owed partially to him, as well.
BurnerMan and PirateMan could be arguably rogue, or a sort of "side-team" collaboration apart from the rest of the unit, given their natures. But for the life of me, I cannot comprehend how any wilderness stage with BurnerMan in it is NOT even being singed. How is that possible?
MM9:
Leader = SplashWoman
Yes, I said it.
Splash appears to be a master manipulator, and has "the voice" for it. Besides that, who's gonna say "no" to somebody wielding the Laser Trident? Anybody? A truly graceful power-player through and through.
2nd in command = TornadoMan
Much like the PharaohMan/SkullMan dynamic, except it's really really obvious. TornadoMan less-than-three's SplashWoman, and would fight to the death for her honor. And of course, he does. It's really all too tragic that Splash doesn't really feel that way about... well, anybody besides herself. TornadoMan motivates and field-leads the team, of course; but always at the mercy of SplashWoman, turning to her for approval for... anything, really!
JewelTran is the only one of the masters that *isn't* captivated by Splash, actually. In fact, I think Jewel kind of dislikes her, if only in bitter envy of having TornadoMan's attention.