Ellen Ripley was just hanging out on the intergalactic transport ship Nostromo leading the mildly-exciting but often-dull life of a Space Teamster when she first realized that she was a badass.
Everything was going fine until once day her idiot Captain decided to land on the remote planet LV-426 to investigate some stupid distress signal the Nostromo picked up, which as we all know is one of the top five most boneheaded decisions any science-fiction space captain can possibly make. So they land on this planet and find this giant destroyed spaceship, and some dumbass fucking crew member decides it would be funny to stick his face in one of the strange egg-like things they find in the smoldering wreckage of this ship. Well, congratulations dumbass - You've now got some crazy fucking alien shit stuck to your face! They finally get the thing detached from this idiot's face, but as you all know that's really only the beginning. The guy then eats some bad Mexican food and a freaking tap-dancing monster busts out of his chest and starts running around the ship burning everything with acid and doing bonghits in the broom closet. The Captain's just like, "I'll handle this little fucker", and starts climbing around the oxygen ventilation ducts like a jackass looking for this stupid little two-foot tall anamatronic teddy bear, when he comes face to face with this:
Turns out this thing is like a seven foot-tall CRAZY AS HELL alien bug-monster that climbs through ducts at light speed, swims faster than Matt Biondi, eats people, spits acid, bites soda cans in half and chops even the most kickass robots into scrap metal and cyborg juice with its prehensile spiked tail. This is what you get for sticking your face in places you shouldn't!
Well this thing starts running around waxing the entire crew one by one. Ripley barely has time to grab a blowtorch, rescue Jonesy the Cat and activate the ship's self-destruct before this crazy-ass alien eats all of her friends. As the only non-pussy on the ship, she's the only one left to get into the escape pod. But things are never easy for badasses like Ripley - it turns out the damn thing somehow snuck into the pod with her when she wasn't looking so she has to kick it in the head Pelé-style like fifty times until it flies out into space.
Ripley gets home and finds out that the stupid corporation she works for had the incredibly fucking brilliant idea of building a human colony on the now-xenomorph-infested LV-426, so she has to go back there with a bunch of tough-ass Colonial Marines and Paul Reiser to "investigate why we've lost contact with the colonists" (read: Kill everything that moves).
So Ripley heads out there with the Marines to bust some fucking football-shaped heads and the shit hits the fan pretty much immediately. Marines are getting eaten by aliens, stuff is popping out of half-dead colonists' chests, face-sucking monsters are scurrying around and through it all Ripley is blasting shit with her bitchin' M-99 assault rifle, taking command of the Colonial Marines and crashing APCs through walls like she's the damn Kool-Aid Man. When Paul Riser is like, "we need to study these aliens and not kill all of them" Ripley's like, "screw you, Paul Riser, you can just go get eaten by them" (and he does). When Bill Paxton starts acting like a little bitch she slaps some sense into him and tells him to stop being such a damn woman all the time and grow a pair. When crap starts getting out of control she decides to nuke the entire planet. When the last surviving colonist chick gets captured by aliens she straps a blowtorch to a grenade-launching machine gun and goes down there to rescue her. Along the way she takes the time out to stare the Alien Queen dead in the face before turning the blowtorch on an entire room full of her crazy alien eggs. Ripley doesn't give a shit that the entire planet's going to be turned to dust in like five minutes - she's the kind of badass who's not going to pass up any opportunity to be a total bitch.
Well obviously this pisses the Alien Queen off, so she hitches a ride on Ripley's ship and starts wrecking everything like a petty diva starlet who gets snubbed at the Grammys trashes her hotel room. This only succeeds at making Ripley EVEN MORE PISSED.
"Get away from her, you bitch!"
What happens next is like the mother of all catfights, with über-hardass Ripley punching the shit out of the bitch Alien Queen with her giant metal robot arms. What's not to like about chicks in 'Mechs battling aliens on a spaceship IN SPACE?? It's so unbelievably kickass it sounds like something that I made up in some insane awesomeness-and-booze-fueled hallucination, and the fact that it's an actual scene from a movie makes my head want to implode from the G-force that the "Awesomeness Field" around my computer is generating. Of course, being the total badass that she is, Ripley beats the Alien Queen's ass and chucks her into space.
Then a shitty movie happened. Ripley shaves her head Sinead O'Connor-style, gets impregnated with an Alien Queen somehow and jumps into some fire to avoid spawning a new generation of Aliens.
She's so notoriously badass though that the jerkass company she works for resurrects her only now she's like half-alien. She runs around on some space station with Winona Ryder and they completely trash the place, killing anything with more than four appendages and beating the crap out of that crazy hybrid alien at the end that shows up for some reason.
Basically, Ripley is one kick-ass bitch. The Aliens seem to have little to no trouble tearing most humans (and sometimes even Predators) new abdomens, but the sheer awesomeness of Ellen Ripley allows her to kick their balls in three out of four times. The best part is that she doesn't even just shoot them to death or incinerate them all the time - she gets into some down-and-dirty hand-to-hand-motherfucking-combat with these crazy things and KICKS THEIR ASSES. The aliens are tough, but she's tougher. Ripley's awesome.