Mandark (Dexter's Laboratory, seasons 1 and 2)

"'Dee Dee…'-His line whenever he sees Dee Dee, whom he has a crush on."

Ivan "Mandark" Astronomonov, his real name being Susan, is the main antagonist of the Cartoon Network series, Dexter's Laboratory. He is Dexter's rival who often seeks to outsmart Dexter to prove once and for all that he is the superior genius. He is voiced by Eddie Deezen.

Why He Was A Good Antagonistic Science Rival

 * 1) Mandark's interactions with the show's main character are interesting and memorable. Like Dexter, Mandark is an intelligent young scientist, and Mandark's growing hatred towards Dexter gives viewers a reason to root for Dexter instead.
 * 2) * Even though he's a rival to Dexter, he usually uses his polite manners and has some respect for Dexter by viewing him as a worthy opponent.
 * 3) He has some memorable quotes, such as his iconic laugh "HA HA HA! HA HA HA HA HA!", "Dee Dee…", or "Yes Dexter, I can read your thoughts and I am smarter than you." from "Dexter's Rival".
 * 4) He is a good inventor and is perfectly capable to invent many things, like making a statue come to life, making robots and so much more.
 * 5) With that said, some of his inventions are quite creative, imaginative, and somewhat impressive when you realize he is a 13-year-old who does all of this rocket science flawlessly and has these science-fantasy-based inventions to rival Dexter's.
 * 6) His crush on Dee Dee is funny, and he often does anything to impress her or help her out, like when he saved her from his traps in the surfing contest in "Sun, Surf, and Science".
 * 7) He is willing to put aside his rivalry against Dexter and team up with him to help save the day, as seen in the episode "Mandarker", when they save Dee Dee from being eaten by the monster JoJo.
 * 8) He was charming and greatly villainous in Mh:greatestmovies:Dexter's Laboratory: Ego Trip, as he teams up with his future selves to take over the world and defeat the Dexters, and this is the only time it works in the story (as the revival seasons handled this rather poorly).
 * 9) He is greatly voiced by Eddie Deezen.

Bad Qualities

 * 1) While his laugh is iconic, it can also come off as annoying.
 * 2) He failed to put his rivalry with Dexter aside when trying to save the Earth from the asteroids in "Let's Save the World You Jerk!".
 * 3) After Ego Trip, he was badly flanderized in the revival seasons, becoming a bland, full-blown "evil genius" stereotype who tries to take over the world. Especially since he becomes significantly more evil, becoming Dexter's arch-nemesis rather than his rival.
 * 4) Even though his talents and competence are equal to Dexter's, but it's implied in Ego Trip that he's not as imaginative as Dexter can be, which limits his genius.