Who's This? A well-timed loser.
How you could have heard of him: The name is at least familiar, because a version of him appeared on the Batman '66 show, which opened the way for the Animated Series to pitch its own version. The latter is explicitly not William Tockman and is the less garish Clock King used as a template for the DC villain to come after Infinite Crisis (in Teen Titans comics). The CW DOES have a William Tockman who commits clock-related crimes, appearing in episodes of both Arrow and The Flash, and played by Robert Knepper.
Example story: World's Finest Comics #284 (October 1982) "When the Old Clock Died!" by Mike W. Barr and Dan Spiegle
Who's Next? A bargain-basement Riddler.