While working on Jonny Quest Real Adventures, Glenn Leopold created villains like Ezekiel Rage, twin daughters of Zin, and Elise.
With Producer Davis Doi, Glenn Leopold developed the Hanna Barbera show "SWAT Kats" for Television.
While working on The Smurfs as Story Editor/Writer, Glenn Leopold created characters like The Clockwork Smurf and Clockwork Smurfette. Glenn Leopold created Clockwork Smurf in Season 1 and Clockwork Smurfette in Season 7.
Glenn Leopold is one of the co-creators of Grandpa Smurf (The Smurfs Season 6) and Nanny Smurf (mentioned in The Smurfs Season 6 and introduced in The Smurfs Season 8).