Villains who are referred to in the very titles of the works in which they appear, whether they are Protagonists or titular antagonists.

Titular and Eponymous are closely related and similar terms, but not always interchangeable.

Eponymous

Means the title contains part or all of a character's name, making that character the eponymous character. Ex. The G Quest; the character G Broson is the eponymous character as part of his name is in the title.

Titular

Means a character is referred to or referenced by the title without using a character name. Ex. Kid vs. Dictator; Harold Graysmith is the titular character of which the Dictator part of the title refers to.