I don't know how many people are aware of the pivotal role he played in Roy Halladay's career. In 2000 Halladay's ERA had balooned to over 10 and he was demoted all the way down to Single A and Mel Queen came out of retirement to work with him......the rest is obviously history. 

He was Blue Jays pitching coach for a four year stretch in the 90s during which Roger Clemens and Pat Hentgen combined for 3 Cy Young awards. He was actively involved in the Jays farm system as well and helped develop guys like David Wells, Jeff Kent, Chris Carpenter, Shawn Green and Mike Timlin among others.