Born in New York City, Shawn was raised by his father, William Shawn, the longtime editor of The New Yorker, and his mother, Cecile, a journalist. After attending high school at The Putney School, a private liberal arts school in rural New Hampshire, Shawn studied history at Harvard University before tackling finance and philosophy at the University of Oxford. In between, he traveled to India on a Fulbright Scholarship, where he spent time as an English teacher. While at Oxford, Shawn began writing plays, making his debut as a playwright with "Four Meals in May" (1967), which he wrote for the university's drama contest. Shawn set up shop back in New York, where he earned a living teaching English, Latin and drama while continuing to write plays. He finally had his first produced play with "Our Late Night" (1975), which staged at New York City's Public Theater and won him the 1975 OBIE Award for Best New Play. Meanwhile, Shawn made his acting debut in his own stage translation of Machiavelli's "The Mandrake" (1977). Two years later, he made a brief, but indelible first impression on screen, playing Diane Keaton's ex-husband in Woody Allen's "Manhattan" (1979), whom the protagonist (Allen) dismisses as a "homunculus."That same year, Shawn appeared as an insurance agent in Bob Fosse's "All That Jazz" (1979), before writing and starring in one of his rare dramatic films, "My Dinner with Andre" (1981), a thinly-veiled autobiographical drama centered around an extended conversation over dinner between friends (Shawn and co-writer Andre Gregory) that became a surprise art-house hit and announced Shawn as both a writer and performer worthy of note. Shawn went on to become a movie fixture of sorts, acting in as many as five films a year by the mid-1980s and logging parts in "Strange Invaders" (1983), "Micki & Maude" (1984) and "Heaven Help Us" (1985). He typically made the most of even the most thankless of parts, as he did in a brief, but memorable bit as the radio superhero Masked Avenger in Woody Allen's "Radio Days" (1987), famously intoning "Beware, evildoers! Wherever you are!" Shawn next delivered arguably his most beloved and lasting performance in Rob Reiner's classic fairy tale "The Princess Bride" (1987), in which he played the Sicilian criminal mastermind Vizzini, who kidnaps Princess Buttercup (Robin Wright) with a master swordsman (Mandy Patinkin) and a hulking giant (Andre the Giant), only to meet his "inconceivable" match in a battle of wits with a mysterious man in black (Cary Elwes). Having already made his presence known on the small screen with guest shots on "Taxi" (ABC, 1978-1983) and a recurring role as the Huxtables' neighbor on "The Cosby Show" (NBC, 1984-1992). Following another OBIE Award win for the rather unpleasant stage drama "The Fever" (1991), Shawn became a favorite of "Star Trek" fans with his oft-hilarious guest stints as the Ferengi Grand Nagus Zek, the financial kingpin of the avaricious aliens and a frequent thorn in the side of Quark (Armin Shimmerman) throughout the series run of "Star Trek: Deep Space Nine" (syndicated, 1993-99). He next reunited with André Gregory to star opposite Julianne Moore in "Vanya on 42nd Street" (1994), an experimental drama in which life starts to imitate Anton Chekhov's classic Uncle Vanya with Shawn playing the title role. In "Clueless" (1995), he played a nerdy high school teacher who finds happiness with another teacher (Twink Caplan), thanks to a nice but superficial student (Alicia Silverstone), a role he reprised on the short-lived sitcom version that ran on ABC during the 1996-97 season. Though the show moved to UPN for another two seasons, Shawn bowed out of the role to pursue other projects, including voicing the insecure Rex the Tyrannosaurus in the animated hit "Toy Story" (1995). All throughout his acting career, Shawn continued to write for the stage, with his play "The Designated Mourner" (1996) premiering in London with Mike Nichols and Miranda Richardson in the lead roles. Director David Hare turned the production into a feature film the following year. Meanwhile, Shawn's always welcome presence enlivened a series of middling comedies, including "Vegas Vacation" (1997) and "My Favorite Martian" (1999), while reprising his voice role as the inept Rex for "Toy Story 2" (1999). Back on television, Shawn enjoyed a couple of episodes on "Cosby" (CBS, 1996-2000) and recurring stint as Dr. Howard Stiles on the crime drama "Crossing Jordan" (NBC, 2001-07). Following a cameo appearance as Rex in "Monsters, Inc" (2001), Shawn did his best as a supporting performer in "Duplex" (2003) and "The Haunted Mansion" (2003). A reunion with Woody Allen in "Melinda and Melinda" (2004) was followed by voicing the demanding boss of Bob Parr (Craig T. Nelson) in the animated hit "The Incredibles" (2004). He next portrayed megalomaniacal industrialist Baron von Westphalen in the dark sci-fi comedy "Southland Tales" (2006), before landing recurring roles on "The L Word" (Showtime, 2004-09) and "Gossip Girl" (The CW, 2007-12). Back to voice work, Shawn once again reprised Rex the Green Dinosaur for "Toy Story 3" (2010), while giving life to Calico in "Cats & Dogs: The Revenge of Kitty Galore" (2010).