Counselor Troi is half-human and half-Betazoid, which gives her diluted telepathic abilities and enormous empathy. As such, Troi's a valuable diplomat and advisor for Picard. Ironically, Troi's personal life is complicated. She used to be involved with Will Riker, and they both struggle to maintain a relationship that's more professional than personal.
Then there are the aliens. They like to control her body, whether that means an unwanted alien pregnancy, channeling their voices through her or giving her unnatural strength (and forcing her to attack Worf).
Troi ultimately is promoted to Commander. She has an unwavering commitment to the crew, and always puts their safety before her own.
Marina Sirtis's Greek parents didn't want her to pursue acting, and after her Next Generation audition, it seemed like they would get their wish. Sirtis didn't think she did well, and was about to fly home to England when she received a call saying the part was hers (although Sirtis had originally auditioned to play Tasha Yar).
For her role as Counselor Troi, she wore hair pieces and dark contact lenses.
Although she's best known for her TV work, Sirtis began her acting career on the stage, and played Ophelia in Hamlet. Her film appearances include Crash and Death Wish 3.
