- For the character's inspiration from the character in The Scooby-Doo Show episode Hang in There, Scooby-Doo, see Johnny (Hang in There, Scooby-Doo).
Dr. Jonathan Jacobo is a former scientist who dressed up like the Pterodactyl Ghost to pull off bank robberies for his experiments to create real monsters.
Jacobo is a middle-aged Caucasian male, with shoulder length dark brown hair with traces of gray in it. He wore glasses during his experiments and when he escaped from prison. His glasses were off when he was unmasked as the Evil Masked Figure.
He's basically a stereotypical mad scientist who plotted to embarrass and destroy Mystery Incorporated through a smear campaign against the gang, and animating the monster disguises of the gang's classics villains, and donning various disguises.
After being defeated by Scooby-Doo and the gang, he was taken to jail, and his subsequent escape resulted in a near-death experience. While in prison, he was cellmates with Jeremiah Wickles, the Black Knight ghost. They hated each other deeply, Jacobo always stole Wickles' tator tots and he got the lead in My Fair Lady.
Scooby-Doo 2: Monsters Unleashed
Years later, he enacted an more complex plan involving the recreation of Scooby's previous monster enemies. Taking on the guise of both Heather Jasper Howe and the Evil Masked Figure, his goal was to discredit Mystery Inc. and eventually destroy them (with the help of Ned). He pinned it all on "Old Man" Jeremiah Wickles and framed him by sending the Black Knight Ghost to and planting the monster book in his mansion. His plan was foiled when Scooby outwitted his monsters and used the control panel to destroy them. This enraged Wickles when he found out, he still had beef with him for taking the lead and stealing his tator tots, both of which Jacobo felt justified as he made a wonderful Eliza, and the tator tots made Wickles feel "puffy." Jacobo and Ned were later taken to prison.
Jacobo: So long, suckers! (glider begins to brake) Agh! Help me, suckers!
Jacobo: I would have gotten away with it... if it weren't for those meddling punks, and their dumb dog!
- The original Pterodactyl Ghost in The Scooby-Doo Show episode Hang in There, Scooby-Doo, was Johnny, who operated a delivery truck, and his criminal activity was about bootleg cassette tapes, not bank robbery. This is such a significant continuity difference that Jonathan Jacobo should probably be regarded as a different character than Johnny, either an AU version or a second criminal who used a Pterodactyl disguise.
Although at the end it's revealed that Jacobo wore a female mask whilst being Heather Jasper Howe, there is a popular idea is that the mad doctor created and used some potions to give himself the a appearance of Heather Jasper Howe before creating the mask.
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