This adman is now a mad man.

Peter Arnell, a Manhattan advertising exec famed for his eccentricities and grandiose airs, has been fired from his namesake business and replaced as head of the Arnell Group by his wife, Sara.

Arnell, 52, has filed a Manhattan Supreme Court suit against the firm and Omnicom, which bought it in 2001, for allegedly refusing to return a million-dollar collection of books and rarities he left in his old 7 World Trade Center office.

Omnicom declined comment.