Longtime “Tonight Show” host Jay Leno returns to Chevalier Theatre for his third Medford appearance. Also an admired stand-up comedian, best-selling children’s book author, much-in-demand corporate speaker, lovable TV and movie voice-over artist, pioneering car builder and mechanic, and philanthropist, Leno is widely characterized as “the hardest working man in show business.” Tickets are $59 to $129 through the Chevalier Theatre website/Ticketmaster. To avoid online ordering fees, purchase tickets at the Chevalier Theatre Box Office, which is open on Fridays and Saturdays from noon to 6 p.m., as well as two hours before every Chevalier Theatre show.