sexual prodigy; stud; Don Juan
Refers to a man with exceptional sexual prowess or a very active sex life. Often used in a somewhat literary or exaggerated way, not an everyday neutral term.
He is called a sexual prodigy by those around him.
The protagonist of that novel is portrayed as a legendary Don Juan.
Compound of 性 (sei, 'sex') and 豪 (gō, 'powerful' or 'heroic'). The exact origin is uncertain, but it likely arose as a literary coinage to describe a man of extraordinary sexual prowess.