Brent Spiner played the beloved Soong-type android Data on Star Trek: The Next Generation, but if it wasn't for Patrick Stewart, the role would have gone to a different actor all together. Premiering in 1987, TNG was Gene Roddenberry's second major series in the Star Trek franchise — a property he had lovingly developed way back in the 1960s. Today, the character Data remains a fan-favorite, and is one of the franchise's most iconic Starfleet officers. Certainly, it's difficult to imagine any actor other than Spiner in the role — but the original plan was for another actor to pay the part.
Data is an iconic Star Trek character, and Spiner's portrayal of the Pinocchio-inspired automaton not only reinforced the robot-who-wants-to-be-human trope in science fiction, but also cemented what would become a core aspect of the Star Trek formula. Data was a continuation of Spock's role as the "logical" voice onboard the Enterprise — often in conflict with the "emotional" voice, Leonard H. "Bones" McCoy. In TNG, this role evolved into the logical non-human character who desires humanity, repeated with characters like The Doctor and Seven of Nine in Star Trek: Voyager and Odo in Star Trek: Deep Space Nine.
Data had such an important role in TNG that he was brought back for the sequel series Star Trek: Picard; in fact, even though his character died at the end of the movie Nemesis. The show was focused on the life of Captain Jean-Luc Picard (Patrick Stewart), but the season 1 plot was actually centered on Data — specifically, his "daughters" that a scientist created based on him (and his positronic brain/matrix). Bringing these two veteran actors back together is especially fitting, even though the two characters were not particularly close, because Stewart was partially responsible for Spiner being cast in the first place — or at least, Stewart's bald head.
Originally, the actor Eric Menyuk was being considered to play Data — by some reports, he was suspected to be in the running for the part; however, after Patrick Stewart was cast as the captain, the production team had doubts about casting Menyuk as a lead — because of his similar appearance. The plan for Menyuk as Data involved the actor shaving his head, which was fine considering the actor had a thinning hairline to begin with. According to a 1987 Paramount casting memo posted to Letters of Note, Stewart was largely competing for the Picard role against more traditional leading men with full heads of hair. In an interview in 2014, Menyuk confirmed that the bald head was the issue, stating: "I like to think that if only Patrick Stewart had hair, I could have been Data."
Menyuk left a positive impression on the TNG production team, and was brought in for a memorable guest role in season 1 as the Traveler: a mysterious being with powers similar to the Q. Menyuk would reprise the role twice more: in season 4 and again in season 7. Although the experience was surely not as thrilling as being a lead in Star Trek: The Next Generation, at least Menyuk was able to contribute to the franchise in a meaningful way.