NFL Connections #35, Answers
The full solution: all four groups and the 16 names, sorted from the easiest group to the trickiest.
Monsters of the Midway ('85 Bears)
Mike Singletary, Richard Dent, Dan Hampton, William Perry
Purple People Eaters (Vikings)
Alan Page, Carl Eller, Jim Marshall, Gary Larsen
Steel Curtain (Steelers)
Joe Greene, Jack Ham, Jack Lambert, Mel Blount
Doomsday Defense (Cowboys)
Bob Lilly, Randy White, Lee Roy Jordan, Cliff Harris