Bar none, the coolest Saturday morning cartoon ever and the greatest cartoon main title sequence. Of course, JONNY QUEST was originally a prime-time adventure series, debuting on ABC in the fall of 1964. It ran a season in prime time, then for eternity on Saturday mornings, weekday afternoons, and even in late night on the Boomerang cable network.
Hanna-Barbera house composer Hoyt Curtin created the swinging theme to JONNY QUEST, which captures the John Barry vibe of the then-popular Sean Connery Bond films and takes it to someplace really special. Cut to Curtin's theme are really kickass action clips based on cartoonist Doug Wildey's designs, including scenes from a short JONNY QUEST tryout film that never aired.
I recently landed a pair of soundtrack CDs (unauthorized, I believe) of Curtin's JONNY QUEST underscore, which is far more sophisticated than other TV cartoon fare and would not have been out of place in an I SPY or MISSION: IMPOSSIBLE.