Every guy named Gary is named after Gary, Indiana. Gary Cooper named himself after the town, and then got very, very popular.
And even before Gary Cooper there were people using it for Gerald (spear power), Gerard (spear hard/brave), and (old) Gerbert (spear bright). It is a cousin to, but believed not historically derived from, Garrett/Garrod. It is unclear whether German/Germain derive from this root or not. It is usually unrelated to Jared (which is usually a Hebrew name, but does have spelling variants that overlap Garrod).