Josh Gibson was a legendary Negro League baseball player in the 1940s. He played for the Homestead Grays.

Fox Mulder was a fan of Gibson and owned a version of his Grays jersey. (TXF: "The Unnatural")

Josh Gibson was referenced indirectly, when his Grays jersey, #20 - GIBSON, was worn by Mulder in the final scene of the episode, "The Unnatural." It is possible that the "Grays" referenced was intended to be the fictional Roswell Grays, with Gibson apparently playing for that team instead.
Interestingly, Mulder asked if a baseball player named "Gibson" was an alien, and Arthur Dales replied, "Bob or Kirk?" disregarding the Baseball Hall of Famer entirely.
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