an 'ugly duckling' that has become a beautiful swan [=an ugly/unsuccessful person or thing that has become beautiful/successful]
('informal') That dog of yours is '(as) ugly as sin'. [=very ugly]
The house is an 'ugly duckling', but it has a lot of potential.
(..) We escaped. The Brotherhood took us prisoner. They sold me to the innkeep. Big ugly fellow. Foul mouth and a face like a half-burnt ham. - The Hound. That's the one. (..)2014 TvShow: Game of Thrones Title: Mockingbird Season: 4 Episode 7