They are actual people who live during the tribulation.
The most poignant verse to answer this question is found in Revelation Chapter 19.
Revelation 19:20
20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
Beyond all the symbolism about the False Prophet and Anti Christ, we see here two individuals that are literally cast into the lake of fire alive. This in and of itself is an accommodation by God in this particular judgment.
Hebrews 9:27
27 And as it is appointed unto men once to die, but after this the judgment: