Justin Verlander - 56.6 WAR
It has been a few seasons since Justin Verlander was traded by the Tigers to the Astros in a rare blockbuster waiver wire move, but wow was he good for Detroit from 2005 to 2017. In 2511 innings in a Tigers uniform, Verlander posted a 3.49 ERA and 3.48 FIP with 2373 strikeouts. Altogether, that totaled 56.6 rWAR and earns him the #2 starter spot in the Tigers' all-time rotation.
Verlander's career accomplishments are unimpeachable as he won Rookie of the Year in 2006, the Cy Young and MVP in 2011, made six All-Star teams as a Tiger, led the league in strikeouts four times, and had numerous high finishes in Cy Young races in addition to his 2011 win all while with the Tigers.
The only blemish on Verlander's tenure in Detroit was that he wasn't ever able to win a World Series ring there despite having a couple of shots at it. The guy misses bats, throws a lot of strikes, and has been one of the best pitchers of this era of baseball.
We still have to wait to see where Verlander stands all-time amongst pitchers in baseball history because he is still going strong after 18 seasons in the league. However, the surefire Hall of Famer locked in his spot in the Tigers' all-time rotation regardless of where he ends up in MLB's pitching pantheon.