This day in history, April 21, 1918, Baron Manfred von Richthofen, also known as “The Red Baron” was killed by Allied fire.
There is some doubt whether it was a shot from the air or from an infantryman on the ground that ended the Baron's career.

A little further in the past:
On this day in history (April 21) 753 B.C. Rome founded
According to tradition, on April 21, 753 B.C., Romulus and his twin brother, Remus, found Rome on the site where they were suckled by a she-wolf.
(it sounds almost like a Klingon myth - except it would have been a targ instead of a wolf)

Yep, the Red Baron apparently was bought down by fire from either an Aussie or a New Zealander Sergeant with a machine gun. I've never heard a theory suggesting he was killed by infantry on the ground.

Thanks for the reminder, PaulS.