Vaughn had acted in a number of TV anthology dramas, but made the switch to series with "The Lieutenant" (NBC, 1963-64), as the superior officer who criticizes star Gary Lockwood to push him to do his best. Vaughn hit the jackpot in popularity with "The Man from U.N.C.L.E." (NBC, 1964-68), a tongue-in-cheek spy show, which followed in the wake of the hit James Bond films. As the smooth and dashingly urbane Napoleon Solo, Vaughn and co-star David McCallum were all the rage as they wore their slickly tailored 60s suits through various adventures. Eight feature films were eventually culled from the series. He also acted in films such as "Bullitt" (1968), and the unjustly overlooked "The Mind of Mr. Soames" (1970), as a compassionate scientist who revives a 30 year-old man in a coma since birth.
A serious and politically active actor, Vaughn wrote "Only Victims" (1972), a study of the Hollywood blacklist resulting from the injustices of the House Un-American Activities Committee after WWII. He also continued his academic studies, eventually earning a Ph.D. from USC, and has long been active in promoting liberal causes.
Vaughn's feature work during the 70s and beyond gradually fell into several categories: routine Hollywood genre fare ("The Towering Inferno" 1974, "Battle Beyond the Stars" 1980), offbeat but little-seen foreign films ("Babysitter" 1975, "The Last Bastion" 1984), and unabashed schlock ("C.H.U.D. II: Bud the Chud" 1989), sometimes redeemed by Vaughn's willingness to camp it up. (His Lord Byron Orlock in "Transylvania Twist" 1989, for instance, invoked Boris Karloff's famous role in "Targets" 1968.) TV work was frequent for the actor, though he never had another hit series. "The Protectors" (syndicated, 1972) rehashed "U.N.C.L.E.", but at least Vaughn had fun on one season of "The A-Team" (NBC, 1986-87) as a general who clearly suggested a retired Napoleon Solo. He was also properly nasty as a scheming businessman on "Emerald Point N.A.S." (1983-84), and has acted in many miniseries and TV-movies, often as clever villains or firm establishment types. Vaughn won an Emmy for his supporting turn in "Washington: Behind Closed Doors" (1977), played Woodrow Wilson in "Backstairs at the White House" (1979) and kidded himself amiably on "Danger Theater" (1993).