Per Memory Alpha:

In 1998, Morello – a die-hard Trekkie – contacted Star Trek producer Rick Berman and asked to have a cameo in Star Trek: Insurrection. Berman agreed, as his son was a fan of Rage Against the Machine. Despite four to five hours of make-up and the high temperature in which they were working (they were filming in the desert), Morello states that he “was on cloud nine because I got to talk to Jean-Luc Picard” (referring, of course, to actor Patrick Stewart). [1]