Clint Howard is a one-man easter egg.
Clint Howard has made five appearances on Star Trek over the years, starting with the original series, where he appeared as a child actor. His most recent appearance was a scene-stealing turn in Strange New Worlds.
That’s 57 years between his first and his most recent appearance. Not even legends like William Shatner or Leonard Nimoy have made appearances over that kind of time span. He also represents a common thread, uniting the three generations of Trek. George Takei, with his surprise appearance on Lower Decks last year, is the only other actor I can think of to appear in all three generations (remember that episode of Voyager?) so Howard is in a very exclusive club, the only other member being Hikaru Sulu himself. But Howard’s 57 years between first and last appearance pips Takei’s 56.
Clint Howard: a shared lineage
Common threads like these are important, as they contribute to the feeling that Star Trek is a continuous shared universe. In-universe references are important, but meta-references like recurring actors make Star Trek feel like a family. One of his appearances was in Discovery, a show whose disregard for canon bordered on disrespect; but seeing a familiar face brought Discovery back into the Star Trek family.
However, Clint Howard is not even close to the actor with the most guest appearances as different characters. That honor goes to Vaughn Armstrong, with 12 appearances across Star Trek: The Next Generation, Deep Space Nine, Voyager, and Enterprise. But where Armstrong is a versatile actor who can disappear into roles, Clint Howard has an unmistakable Clint Howard vibe about him, making his appearances even more like a continuous thread in the tapestry that is Star Trek.