Isaac Watts. Dude wrote over 600 hymns! Including "When I Survey..." which purportedly Charles Wesley himself said he would trade all *his* hymns to have written. Also wrote one of my favorite songs on Sandra McCracken's "Builder and Architect" album, "I Boast No More."
He wrote "Joy to the World"- have you BEEN to a Christmas service that doesn't sing that song?
Oh, and he died almost 300 years ago.