"Open Wheel" is a big category and is objectively impossible to narrow the field down to just 4. My intent is not to go too far afield but for the sake of fairness I feel specific open wheel categories are necessary.
Indy Car is obvious to anyone who has any sense of history:
A.J.
Mario
Big Al
Rocket Rick
Silver Crown is almost as obvious as Indy Car:
Jack
Chuck
Cody
Sills
Sprint Cars is where it gets very dicey but there are a couple that are obvious:
Steve Kinser
DD
Donnie Schatz
Jack Hewitt---------Jack is in two categories because #1. We all love the guy. #2. He won a ton of races driving both wing cars and wingless cars against some very tough competition in both types of cars.
Midgets are almost as dicey as Sprints but again, a couple are obvious:
Mel Kenyon
Bob Tattersall
Stan Fox
Rich Vogler