Rounding out the original trio of companions is science teacher Ian Chesterton. The creators of Doctor Who conceived of Ian as the traditional hero of the show, with the burden of carrying most of the action of the stories falling on his shoulders. The Doctor was much more of a menacing, untrustworthy figure in the early days - for instance...
...here's Ian in the first story, An Unearthly Child, after stopping the Doctor from bashing an unaware caveman's head in with a rock. So yeah, originally, the hero of Doctor Who was meant to be Ian, not the Doctor. And considering he was a fairly stuffy, buttoned-down, secondary school science teacher, Ian took to the action hero role surprisingly well.
Here he is in The Daleks, being shot. Ok, bad example. He does later scoop the nasty-ass Dalek mutant creature out onto the floor and then crawl inside its shell to use it as a disguise. That's pretty hard core.
Here he is...I don't know, singing?...in Marco Polo. Let's move on.
Ok, here we go. Here he is in The Aztecs, fighting with Ixta, their mightiest warrior. He kills Ixta in this fight, hurling him to his death from the top of a pyramid. Fuck yeah!
Here he is as a galley slave in The Romans. Later, these two become gladiators, but when Ian's matched up against his old pal Delos here, the two instead turn on their captors and manage to fight their way out of the arena to freedom.
Here he is in The Crusades being knighted by Richard the motherfucking Lionhearted for sheer awesomeness.
Later in the same story, while on a mission to rescue Barbara from Saladin, he gets tied up by a bandit who springs the old honey-and-anthill trap on him. Ian still manages to overpower the guy and then talks him into helping him find Barbara. Ian will kick your ass and then force you to be his friend!
But there was more to Ian than teaching science and killing historical figures. Ian was very protective of Barbara, Susan, and (after they threw Susan overboard) Vicki. He had a fatherly relationship with the younger girls, and a...less fatherly relationship with Barbara. Although early on Barbara enjoyed the occasional fling with the odd Thal or French counter-revolutionary, Ian remained steadfast in his devotion to her, and from The Romans on it was clear that they were totally doing it.
Barbara and Ian finally found their way home thanks to a stolen Dalek time-ship. He didn't appear on the show again, but Sarah Jane Smith recently suggested that he and Barbara are now married and haven't aged since the '60s. He is presumably still kicking ass whenever anybody looks at his wife cross-eyed. Ian Chesterton - most unlikely action hero ever.