A documentary by Mary Kerr. Unrated. Opens Friday, October 25, at the Cinematheque

Born Craig Castaldo (a name he always hated), Radioman is physically small and has devoted himself to a very narrow dream: to live on the edge of New York movie sets and ingratiate himself with actors and film crews.

“Sometimes it’s a tidal wave of fun,” he says at one point, in this brief but wide-ranging documentary. “Other times, it’s a monsoon of misery.” That’s probably a line from one of the films he saw being shot or, more likely, from the massive VHS collection he keeps in his cockroach-laden lair in Brooklyn. Back when he was drinking, Radioman was homeless, but a stint at infamous Bellevue Hospital convinced him to trade booze for craft services, and he became a welcome fixture—that trademark radio always hanging around his neck—on sets he had previously approached belligerently.

Something about his bearded-leprechaun demeanour—childlike awe coupled with a foul mouth, you could say—was enjoyed by performers of the more outgoing sort. Robin Williams, the celebrity he most resembles, is the most articulate when talking to first-time doc maker Mary Kerr about the phenomenon, while macho dudes like George Clooney and Matt Damon are seen being especially effusive toward him. Tilda Swinton, Meryl Streep, and Sandra Bullock also interact playfully with the little guy. (One of his most rewarding skills, it seems, is the ability to keep those interactions brief.)

IMDb gives Castaldo credit for bit parts in a dozen features, semiregular spots on 30 Rock, and a starring role (as himself) in an upcoming short. But there is little indication he could expand his persona beyond that of mildly beloved hanger-on. Radioman never quite gets under the skin of its subject to find deeper motivation. Perhaps there is none.

Its most melancholy sequence follows him to Los Angeles, where—despite his brand-new tux and clean baseball cap—he fails to get into the Academy Awards. Standing behind the massive crowds outside, he can’t believe so many people would waste their time taking pictures and asking for autographs.