Maybe not quite as awesome as some of these other stories, as this is my first serious fort, but here goes.
For about a year there had been humans laying siege to my fort. I finally decided, running low on wood, that enough was enough. The siege force was 20 humans, all wearing iron armor with no ranged capabilites, with one of them mounted. I figured I'd take a stab at sending my squad of high quality steel equipped Legendary speardwarves out to mop them up. So I set military only outside, lower my drawbridge, and station said squad on top of the human camp site...and quickly notice something wrong, one of my marksdwarf squads is moving, and I realize I've dispatched the wrong group! Immediately changing their station orders I breath a sigh of relief as they turn around...all but one.
Amost Furnacehealers, lover of my captain of the guard/legendary speardwarf squad leader, is still marching towards the enemy, apparently on a mission. Wearing middling quality steel chainmail, and with his crossbow in hand, to what I thought would surely be his death, as he was only midway up on his hammer skill in the event he ran out of ammo. In what is probably an important thing to note later, said captain of the guard apparently decided that killing some random criminal dwarf was more important right that moment than her husband marching to his doom, turned around back into the fort, taking the rest of her squad with her. So, one marksdwarf versus 20 armed humans...and a victory!
5 humans shot or bludgeoned to death, the remaining 15 routed, and no wounds to my now titled hero, Amost Furnacehealers the Helmed Comet of something, the rest of his title is cut off. Epic enough story for my first 6 years in my first fort, I'd say