Star Trek: The Next Generation's Deanna Troi was a crucial member of the cast, but she almost departed the show at the end of the first season. Launched in 1987 - at the height of the popularity of the films starring the cast of Star Trek: The Original Series - The Next Generation jumped forward a century to focus on a new Enterprise with a new crew. Despite the fact that longtime fans initially shunned the show, TNG became a huge hit in syndication and launched a Star Trek television empire that would last for over fifteen years.
Star Trek: The Next Generation's first season was infamously fraught with problems. The show had an impressive cast and production design, but the writing was not up to snuff, largely due to the rapidly declining health of series creator and executive producer Gene Roddenberry. The fact that characters like Captain Jean-Luc Picard and Lieutenant Commander Data were able to cut through that first year is more a testament to the abilities of the actors than the writing staff, which was in constant flux until the third season.
Issues with the quality of the writing very nearly cost a TNG cast member their job too. The producers had planned to write out Counselor Deanna Troi (Marina Sirtis) after the show's first season concluded; the writers were never quite sure what to do with the psychic therapist on the bridge and were ready to chalk up Troi to a first season misfire and move on.
Fate would have other plans though. Denise Crosby, who played Tasha Yar for most of season 1, decided to leave midway through the first year due to a lack of character development and compelling stories. Not long after, Gates McFadden - who played Doctor Beverly Crusher - abruptly quit after clashes with producer Maurice Hurley (McFadden would return in season three when Hurley left). The producers realized losing the entire female contingent from the first season would be a seriously bad look, so Troi was ultimately saved.
Deanna Troi would of course go on to become an integral part of Star Trek: The Next Generation. She would often serve as Picard's conscience, a confidant without equal for the good captain. The writing for the character would improve in later seasons in episodes like "Face Of The Enemy," where she went undercover as a Romulan agent to help Spock complete an important mission on Romulus. Sirtis gave arguably her best performance as Troi in the recent Star Trek: Picard episode "Nepenthe," bringing a new level of pathos to the character without betraying what made her work in the first place. Deanna Troi is a foundational Star Trek character, and it's baffling to realize she was almost retired before she even got started.