Alex Ripley was for the first three movies basically a scientist that was the reluctant soldier. In the first movie she works as part of the crew of the nostromo, a corporate space vessel. She eventually defeats the alien that is onboard with her wit and hurls the creature out into the vastness of space..

In the second movie she is sent as a scientific advisor to aid in the colonial marine investigative endeaver on a colony that is no longer being heard from. She is first quick to point out that weapon fire near the reactors of the colony could result in meltdown. Thus she basically disallows the use of heavy firepower because she fears a reactor breech. But after she sees the dangers even she is off using pulserifles and flame throwers. She even attacks the alien queen; burning many of her eggs and kills the alien queen.

In the third movie she is at a penal colony without weapons or means of help. She still maintains her scientific mannerisms but assumes more of a leadership role in the fight against an alien that is loose on the colony. She dies in the end because of a conviction that prevents her from wishing to continue to carry an alien embryo in her body for future corporate exploitations

In the fourth movie Ripley is reborn. She is cloned from DNA material of the former dead Ripley. This new Ripley has some alien DNA and consequently is faster, tougher and stronger than before. She is a fighter now of the highest degree.

Ripley as the perfectly constructed warrior in Alien 4
Is she ready to be in an Alien 5 though?

Ripley torching the Queen Alien's Eggs in Aliens

Ripley up close and personal
with the Alien in Alien 3

images on this page courtesy 20th century Fox