Ike, from Fire Emblem Path of Radiance and Radiant Dawn. Sure he has 'support,' but by the end of the first game he can usually fend off a whole enemy squad single handedly without breaking a sweat. Then in the second game he's that powerful when you first get him.
Also, he fights for his friends.
But really any character from almost any game where Co-op is not an optional gameplay mode. Once you add 1 to 3 other characters that could, if you choose, be human controlled then you could be overwhelmed if you tried it solo. (though they usually decrease the difficulty when you do) (some exceptions apply)
Which is why I'd always thought that'd be cool for The Star Fox games, because I always end up saving everyone at least once during my fight to take down entire space armadas single handedly.
Until Star Wolf shows up on Venom.