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

In context
10They had tails with stingers like scorpions, which had the power to injure people for five months.
11They were ruled by a king, the angel of the Abyss. His name in Hebrew is Abaddon, and in Greek it is Apollyon.
12The first woe has passed. Behold, two woes are still to follow.
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Berean Standard Bible · A modern, readable English translation. Public domain (CC0).