When did Rob Grill grow his mustache?

Rob Grill, the lead singer of the band The Grass Roots, became well-known for his distinctive mustache in the late 1960s and early 1970s. While there isn't a specific date recorded for when he first grew it, it became a signature part of his look during the height of the band's popularity. His mustache contributed to his image as a classic rock icon of that era.