Peter Jackson appeared briefly in each of his trilogy's films:

The Fellowship of the Ring (2001): as drunken peasant Albert Dreary eating a carrot, and a citizen of Bree

The Two Towers (2002): as a Helm's Deep guard, costumed in chain mail as a Rohirrim Warrior, and throwing a gold-tipped spear to defend the gate

The Return of the King (2003): as the boatswain or pirate captain of a Corsair of Umbar ship

Jackson also made brief cameo appearances in Bad Taste (1987) as Derek/Robert, in Dead-Alive (1992) (aka Braindead) as the Undertaker's Assistant, in Heavenly Creatures (1994) as a panhandling Bum outside a theatre who was kissed by Juliet Hulme, and in The Frighteners (1996) as a Biker Man with Piercings

Martin Scorsese as the uncredited gunman Jimmy Shorts who shot "Johnny Boy" (Robert DeNiro) and Charlie Cappa (Harvey Keitel) at the end of the film from the back seat of a car; to add another layer of meaning, he was also visible for a split instant in a "portrait" of Charlie in the opening flashback of home movies/main title credits sequence, and Scorsese also served as the interior voice of Charlie when he was kneeling and praying in church in one of the film's earlier scenes -- delivering the off-screen narrated line: "Lord, I'm not worthy to eat your flesh, not worthy to drink your blood."

Writer/director/producer Richard Linklater (in his debut film) in an odd character role as "Should Have Stayed at Bus Station." He was the first on-screen character, who emerged from a Trailways bus in Austin, Texas, and then hopped into a Roy's taxi cab, where he hassled the indifferent, bored driver with a description of a weird, empty dream he had just had (in which "nothing was going on at all" - he was just reading and flipping through TV stations), and a strange monologue about the crossroads' decision of Dorothy and the Scarecrow in The Wizard of Oz (1939), expressing his manic, stream-of-consciousness belief that each alternate path or direction not chosen acquired a life of its own ("All those other directions, just because they thought about it, became separate realities").

Leonard Nimoy (in his directorial debut) reprised his role as a newly-regenerated Captain Spock, through the Genesis Effect after his katra (living soul) was restored from Dr. Leonard McCoy (DeForest Kelley) in a ritualistic refusion ceremony called fal-tor-pan on the planet Vulcan; he began to remember his past in the film's finale as he stood face-to-face with old friend Admiral James Kirk (William Shatner), telling him: "Jim. Your name is Jim," to which Kirk replied simply: "Yes" as the film ended.

Nimoy also directed himself in a larger role as Spock in the blockbuster Star Trek IV: The Voyage Home (1986).

Martin Scorsese portrayed a lunatic cab passenger, a scary-acting, mustached, middle-aged individual who insisted that Travis Bickle (Robert DeNiro) pull over to the curb, keep the meter running, and just sit. He was the agonized husband of a cheating wife who watched her scantily-clad silhouette in the lit second-story window of another man's apartment, and described a homicidal plan - a fantasy of murdering his adulterous wife and her black partner with a .44 Magnum.

Scorsese also has brief cameos in Raging Bull (1980) as a Barbizon stagehand, The King of Comedy (1983) as a TV Director, After Hours (1985) as a Club Berlin Searchlight Operator, The Color of Money (1986) as the opening voice-over Narrator, The Age of Innocence (1993) as a Photographer, Bringing Out the Dead (1999) as the Voice of a Dispatcher, and Gangs of New York (2002) as a Wealthy Homeowner.

Orson Welles had a bit role as a trial advocate named Hastler, who reprised the opening parable of "The Man and the Country" to Joseph K (Anthony Perkins) at the climactic moment of the film.