He pioneered a number of forms that have been with improvisational theatre companies ever since -- most notably the improvised press conference. He also was the author of the original scenario -- "Enterprise" -- the served as the pilot for the Compass. In other words, he wrote an outline of a stage story and a group of actors, using improvisational techniques, built on a play on it. It was the success of "Enterprise" -- given as an experimental production at the University of Chicago -- that convinced David Shepherd and Paul Sills that this form could be the basis of an ongoing theatre. The Compass, of course, was the rough version of what later became Second City.
He was a talented writer and grew from an awkward but earnest actor into a brilliant comic performer. Those who attended the Second City reunion at the University of Chicago in 1976 will have particularly strong memories of his turn as Henry Kissinger. A sample: "Then President Nixon said to me, 'Henry, let's kneel down together and pray to God. You in your way, I in His."
Among the general public, he was probably best known as Henry Blake in the film MASH. It was through improvising that he and Gary Burghoff came up with the bit of Radar repeating Blake's orders in counterpoint to the supposedly senior officer. Of course, this turned into the running bit that Burghoff used with the TV Henry Blake, the late MacLean Stevenson.
Roger was an improvisational pioneer and a very nice man.