If I understand correctly, the version you saw on WGN-TV was Bob Bell, but credit still goes to Larry Harmon for coming up with the blueprint and being enough of a businessman to franchise Bozo.
Not to speak ill of the recently departed but Harmon was occasionally known to take credit where none was due. His induction into something called the Clown Hall of Fame was rescinded because of controversies surrounding some of his more dubious claims.
Don't even get the Laurel & Hardy* fans started on how he damaged their legacy through his (mis)controlling of their likenesses. There are bitter feelings held by Stan Laurel's survivors to this day not to mention a whole host of Sons of the Desert that curse his name whenever its mentioned.
Bob Bell**, Frazier Thomas, "Cookie" and the rest of the crew that made the WGN Bozo Show so iconic are the ones who will live on as fond memories.
* When the US Post Office put L&H on a stamp several years back Harmon tried to get financial compensation. The government essentially told him to pound sand.
** Harmon refused to allow Mr. Bell to dress up as Bozo when the latter was inducted into the Clown Hall of Fame. It takes a small, petty man to deny someone else their rightfully earned glory.