Marty could hear someone greeting Hubert by name outside of Emmett Brown's livery stable, and Doc advised Marty noted that Hubert was the Mayor of Hill Valley. Marty saw Hubert again at the Hill Valley Festival, when the mayor presided over the dedication of the new clock.
In the DVD commentary to Part III, Bob Gale confirms that the part was offered to former President Ronald Reagan, by way of Reagan's former movie agent and friend, Lew Wassermann. However, Reagan politely declined. Had Reagan accepted, it would have been his final film role.