The number one spot needs to go to, well, Spot. Starting with TNG's season 4 episode "Data's Day," Spot is Data's (Brent Spiner) loyal companion for the rest of the series, as well as appearing in 1994's Star Trek: Generations and 2002's Star Trek: Nemesis. Spot gets along with Data better than she does any human, and the feeling is mutual — at least they are as soon as Data has feelings.
While it isn't the most beloved Star Trek movie, Generations includes one of the franchise's most touching moments, thanks in part to Spot. Towards the end of the film, Data discovers Spot is alive amidst the wreckage of the Enterprise-D. Having a new chip that gives him human emotions, Data cries tears of joy. The sensation is so strange to him that he believes the chip is malfunctioning.
And if you're curious about what happens to Spot after Data's death in Nemesis, the film's special edition DVD includes a deleted scene that reveals Spot finding an unlikely caregiver. Worf (Michael Dorn) and Geordi (LeVar Burton) are tasked with cleaning out Data's quarters. As they do, Spot emerges, climbs onto Data's desk, and jumps into Worf's arms. The Klingon says, "I am not a cat person." Smiling, Geordi answers, "Looks like you are now."
