By the time Shark Tank entered its fourth season in 2012, the show had solidified its cultural footprint. Mark Cuban, Daymond John, Kevin O’Leary, Barbara Corcoran, Robert Herjavec, and later Lori Greiner (who became full-time in Season 3) were the household names. But to keep the tank fresh—and fill occasional absences—the producers introduced a rotating panel of guest sharks . Seasons 4, 5, and 6 (airing 2012–2015) featured some of the most memorable and effective substitute investors. Season 4 (2012–2013): The Rise of the Rotating Seat Season 4 saw the first major use of guest sharks, partly due to Robert Herjavec’s reduced availability as his cybersecurity company went public.