the.com/fat cat

means A wealthy, powerful person, especially a business executive or financier viewed as privileged and self-indulgent.

from American slang from the early 20th century, first used to describe rich political donors — men bankrolling campaigns from the comfort of their wealth. The image is simple and unkind: a cat fed so well it's grown sleek, slow, and smug, too comfortable to bother chasing anything anymore.