There’s an excellent piece in the NY Times about Leonardo Da Vinci’s obsession with drawing weird faces:
Leonardo was a true Renaissance man, fascinated with everything — the mechanics of flight, architecture, engineering, botany, artillery and human anatomy — but one of his favorite private pastimes was to draw faces, either as scribbles in the margins of his notebooks or as fully conceived sketches later used for paintings.
Leonardo da Vinci made ugly beautiful, an approach Francis Bacon did well to mimic nearly five hundred years later.