Apollyon appears in the New Testament (Book of Revelation 9:7 – 11) leading the locust-like swarm of demons that will be released in the End Times:

7. In appearance the locusts were like horses arrayed for battle; on their heads were what looked like crowns of gold; their faces were like human faces, 8. their hair like women’s hair, and their teeth like lions” teeth; 9. they had scales like iron breastplates, and the noise of their wings was like the noise of many chariots with horses rushing into battle. 10. They have tails like scorpions, and stings, and their power of hurting men for five months lies in their tails. 11. They have as king over them the angel of the bottomless pit; his name in Hebrew is Abaddon, and in Greek he is called Apollyon.