R8-B7/Legends

R8 was Mace Windu's astromech droid. He was destroyed on Vanqor by a gundark when it pulled off his head, while Mace Windu and Anakin Skywalker were searching for survivors at the crash site of the Endurance.

Behind the scenes
If R8 is indeed an R8-series astromech droid, and not just an earlier model with an "R8" designation, his inclusion poses a continuity problem, as R8 units had not been created until after the Galactic Civil War.