Here are a few examples:
* Daria: The cynical and sarcastic teenager from the MTV animated series "Daria."
* Dexter: The genius boy who invents amazing gadgets in his secret lab in "Dexter's Laboratory."
* Donald Duck: The famous Disney character known for his quacking and temper.
* Daffy Duck: The wacky and mischievous Warner Bros. character, known for his "sufferin' succotash" catchphrase.
* Doug: The lovable and sometimes clumsy boy from the Nickelodeon series "Doug."
* Danny Phantom: The teenage superhero with the ability to turn into a ghost in the Nickelodeon series "Danny Phantom."
* Dipper Pines: The adventurous and curious protagonist of the Disney series "Gravity Falls."
* Duffy Duck: The friend and sidekick of Mickey Mouse and Donald Duck.
There are countless other cartoon characters starting with D! Which one did you have in mind?