monomaniac

Same as monomaniacal.

A person affected by monomania.

In law, one who is insane upon some one or more subjects, and apparently sane upon all others.

A person affected by monomania.

Affected with monomania, or partial derangement of intellect; caused by, or resulting from, monomania.

A person who is obsessed with a single thing, to the exclusion of other concerns.

Focussed on one thing above all others.

a person suffering from monomania