The Sun reports Rountree, who worked as the group's musical director for more than 30 years, died Sunday in a Las Vegas hospital.
Rountree, known simply as Tree, also performed other roles for the group, including arranger, composer and keyboardist.
Rountree, a Detroit native, performed with some of the music industry's biggest stars, including the Temptations, Gladys Knight and the Pips, Mary Wilson, Martha Reeves, Frankie Valli, Bill Withers, Freda Payne and David Ruffin.
