I discovered these two illustrations of the 1925 Indy 500 in the June 1925 issue of Popular Mechanics. Interesting to note the wooden surface the cars raced on that year as shown in the bottom image.
DePaolo has the honor of winning the first Indy 500 where the average a speed of the participant cars was over 100 mph. He also nearly had the honor of killing Adolph Hitler in the 1934 Avus race outside of Berlin. During that race DePaolo's car threw two connecting rods which barely missed Hitler who was watching from a track side box. That definitely would have been the biggest racing achievement ever!