Simplify the following text for a Grade 7 native English-speaking person.
Original: Stephen Arthur Stills ( born January 3 , 1945 ; Dallas , Texas ) is an American guitarist and singer\/songwriter best known for his work with Buffalo Springfield and Crosby , Stills & Nash ( and Young ) .
Simplified: Stephen Stills ( January 3 , 1945 - ) is an American singer and songwriter . He is most famous as a member of the groups Buffalo Springfield and Crosby , Stills & Nash .