John Sebastian

John Sebastian (born March 17, 1944) is an American singer and songwriter. 
The Lovin' Spoonful.
His career first started in 1965 as the leader of the folk-rock band The Lovin' Spoonful. The group had popular songs such as "Summer in the City" and "Do You Believe In Magic?". Sebastian left the band in 1968. 
Solo.
John played at the Woodstock Festival in 1969, where he performed the Lovin' Spoonful song "Darling Be Home Soon". 
He wrote and sang the opening theme song for the 1970s sitcom "Welcome Back Kotter".