Ellen Ripley

Ellen Ripley is the main protagonist of the Alien series, and the archenemy of the destructive alien race, the Xenomorphs, who took about everything she ever loved.

Alien
Ripley was a member of the Nostromo, working for the Compagny. The ship goes on an abandoned planet in a rescue mission, but there is no one to save. One of the crew members gets attacked by a creature from a mysterious egg. Despite Rypley's objections, he is brought back in the Nostromo. As a results, the first Xenomorph ever shown is born, and starts killing off all the crew one by one.

Ripley eventually escapes and gets the Alien sucked into the vaccum of space. She sets off for Earth.

Aliens
Ripley awakens from hypersleep after 57 years, and is horrified to learn that her daughter died of old age. She is forced to go on a planet colonized by the Aliens, and faces an army of Xenomorph, including their Queen, to protect a little girl, Newt.

Alien 3
After escaping again, Ripley's ship crashes on a prison planet full of crimminals (to add more tragedy, Newt is killed in the crash). As a new sort of Alien starts killing the convicts, Ripley discovers she is pregnant of an Alien Queen, whom the compagny wants at any cost to use the Xenomorph as an army (like in the previous films). Ripley sacrifies herself, killing both her baby Xenomorph and the Dog Alien in the process.

Alien Resurrection
Ellen Ripley remains dead in the fourth film, but the compagny cloned her several time in order to obtain also a copy of the Alien Queen' DNA. The last and most successful clone, called Ripley 8. She is different from her model as she is more sexually open, more cynical, and feels more empathy toward the Aliens. She also inherited some of their powers, like acid blood.