No. 4 Roger Clemens
Clemens only played two seasons north of the border, but they were ridiculous. To quickly put his talent (albeit fueled by PEDs during that era) into perspective, his 20.1 bWAR ranks seventh amongst starters in Jays history, in just two seasons!
The Rocket signed a four-year, $40M deal with the Blue Jays after the 1996 season after cementing himself as one of the best pitchers in baseball history with the Boston Red Sox. His 1997 and 98 seasons were ones for the ages. He won back to back Cy Youngs, leading the AL in ERA, wins, strikeouts, and FIP both of them. His 1998 season also saw him lead the AL in H/9, K/9 and HR/9.
Clemens requested a trade prior to the 1999 season, as he didn’t believe the Blue Jays to be competitive enough going into that year. Clemens would go on to win two World Series’ with the Yankees, but not after putting up arguably his two best seasons of his career with the Blue Jays. This could at least be true about 1997, as his 11.9 bWAR was the single highest of his career. For reference, Aaron Judge’s mark from last year was 10.6. Clemens’ exploits on the mound trumped that of a 62 homer season.
Clemens’ Blue Jays career wasn’t a long one, but by performance alone it deserves recognition. Clemens is one of the most talented, but polarizing pitchers in the history of the sport, and still represents an interesting blip on the franchise's history.