Who led an all black american cavalry unit at the battle of san juan hill?

First Lieutenant Jules Garesche Ord ordered the advance of the Buffalo Soldiers (black members of the 10th Cavalry Regiment).

Ord (a white officer) died in the attack.  But the efforts of the Buffalo Soldiers and his leadership are credited with the success of the battle.  One of Teddy Roosevelt's "Rough Riders" said of the Buffalo Soldiers and their dedication: "I never saw braver men anywhere."