In 1969 Ken Tatum, an Angels rookie, had the best season by a relief pitcher (as measured by the Win-Shares statistic) in franchise history. He did not even make his debut until May 28. His 22 saves and 65 strikeouts in the 69 season give only a glimmer of his accomplishments - finishing 4th in the Rookie of the Year voting and 29th in the league MVP race might add a little more to the luster, but consider his ERA of 1.36 when the league average was 3.45 - and recall that the 1969 season was also when baseball's rule changes took the mound back from the pitchers. To dominate in that season was a special accomplishment.
The Win Shares discovery was first published by esteemed Angels historian/fan Matt Welch at his blog, where you can read more about Tatum's place in Angels' statistical lore.
Ken Tatum pitched for two seasons with the Angels and still ranks in 9th palce on the franchise saves list with 39 saves. He was traded along with Doug Griffin and Jarvis Tatum (no relation) to Boston for three players, one of them being Ray Jarvis, making it the only known MLB trade where two players with the same last name were traded for a player whose last name was the first name belonging to one of those two players.