We first met Hikaru Sulu when Star Trek: The Original Series aired all the way back in 1966. But that first name of his? Turns out he never had one until 1981—one that didn't even become part of the Trek canon until mentioned on screen in 1986 during Star Trek IV: The Voyage Home.
And the reason Sulu finally got a full name?
As novelist Vonda McIntyre explained about her 1981 Trek tie-in novel The Entropy Effect:
The only potential glitch in the Star Trek books came about because I couldn't figure out how to write a love scene where the protagonists called each other by their surnames. So I gave Mr. Sulu a first name, "Hikaru," which is from The Tale of Genji. I was blissfully unaware of the glitch till long after the fact; someone at Paramount objected to the idea of the character's having a given name, for reasons unclear to me. David [Hartwell, the book's editor] had the good idea of asking Gene Roddenberry and George Takei their opinion, and both of them said "Go for it" or words to that effect. And so Mr. Sulu has a first name.
But even that, however, wasn't enough for the name to be accepted as part of Star Trek canon. That only occurred with Star Trek VI, thanks to Peter David, who was writing the movie's comic-book adaptation. During a visit to the set, it was David who convinced director Nicholas Meyer to incorporate the name into the film.