He appeared in 220 plays (including Glengarry Glen Ross), 38 movies (including The Natural, Thief, Dead Man Walking and Mrs. Doubtfire) and hundreds of television shows. He stepped in as the desk sergeant in Hill Street Blues after the untimely death of Michael Conrad in 1984, a few years after turning down the role of "Coach" on Cheers that eventually went to Nicholas Colosanto. His signature line on Hill Street Blues: "Let's do it to them before they do it to us."

http://www.usatoday.com/life/people/2008-12-10-prosky-obit_N.htm