This name is particularly common in SFF, the most recent example being the character of Galen Erso in Rogue One.
But a quick browse of the Wikipedia disambiguation page on the name Galen corroborates that the name is overwhelmingly popular in SFF:
Galen, a technomage in the Babylon 5 universe (SF)
Galen DeMarco, a character in the world of Judge Dredd (SF)
Gal'en Kord, a character in the Transformers universe (SF)
Galen Tyrol, a character in the re-imagined Battlestar Galactica TV series (SF)
Galen Doc Adams, a character of the lead cast of Gunsmoke, a long running radio and subsequent TV series.
Galen, the assistant of Dr. Zaius in the 1968 film Planet of the Apes and subsequent TV series (SF)
Professor Richard Galen, a character in the Star Trek: The Next Generation episode "The Chase" (SF)
Galen Marek, a character in the Star Wars: The Force Unleashed project (SF)
Galen, a character in the TV Series Roar (Fantasy)
Dr. Galén, a character in a play The White Disease by Karel Čapek and in its movie adaptation Skeleton on Horseback
Dr. Galen Erso, a character in the movie Rogue One: A Star Wars Story. (SF)
Plus, already mentioned:
Dr. Galen, in-universe proposed name for the doctor on Star Trek: Voyager.
Additionally, noted by others:
Galen the Skill master from Robin Hobb's Assassin's Apprentice (Fantasy)
Parth Galen, a green lawn near the Falls of Rauros on the River Anduin, where the Fellowship of the Ring was broken in the LOTR universe (Fantasy)
Ser Galen, a Komarran terrorist from the Brothers in Arms from Lois McMaster Bujold's Vorkosigan series (SF)
What is the relationship among the many uses of the name "Galen" in sci-fi?
(Sorry, I'm not going to answer this in poetry)