In Revelation 9:11, what is the Hebrew name of the angel of the Abyss?

Answer: Abaddon

The locusts' king is the angel of the Abyss; his name in Hebrew is Abaddon, and in Greek, Apollyon.

“They were ruled by a king, the angel of the Abyss. His name in Hebrew is Abaddon, and in Greek it is Apollyon.”— Revelation 9:11 (BSB)