Well is an adverb followed by another descriptive word known. They combine to form one idea modifying the noun"actor' The actress who accepted her award was well known A well known' follows the noun describes, so a hyphen is not used. A friendly looking man approached me yesterday asking for the nearest post office. Friendly looking' is compound adjective modifying the noun'man' Emma is a friendly little girl, 'Friendly little' is not a compound adjective, but adjectives modifying the noun girl