In Revelation 19:20, who was captured with the beast and thrown alive into the lake of fire?

Answer: The false prophet

The beast was captured along with the false prophet who had deceived people with signs; both were thrown alive into the fiery lake.

“But the beast was captured along with the false prophet, who on its behalf had performed signs deceiving those who had the mark of the beast and worshiped its image. Both the beast and the false prophet were thrown alive into the fiery lake of burning sulfur.”— Revelation 19:20 (BSB)