What position did Mike Singletary primarily play?

What jersey number did Aaron Donald wear with the Rams? What position did Dick Butkus primarily play? Which college was Dick Butkus playing for when he entered the NFL? What jersey number did Dick Butkus wear with the Bears? Mike Singletary is best known for playing with which NFL team? Which college was Mike Singletary playing for when he entered the NFL? What jersey number did Mike Singletary wear with the Bears? What position did Jack Lambert primarily play?