The Nobody is actually the Lord of the earth before whom the two witnesses stand, and serve.
He is the rider of the white horse, whom the other horsemen of the apocalypse follow and serve.
There are actually 5 horsemen, and not 4, mentioned in the book of Revelation.
1. the rider of the white horse (the Lord of the earth having the seal of the living God),
2. the rider of the red horse,
3. the rider of the black horse,
4. the rider of the pale horse named Death,
5. Hades, who closely follows Death
These 5 horsemen are the same 5 angels mentioned in Revelation 7:
1 After this I saw four angels standing at the four corners of the earth, holding back the four winds of the earth to prevent any wind from blowing on the land or on the sea or on any tree. 2 Then I saw another angel coming up from the east, having the seal of the living God. He called out in a loud voice to the four angels who had been given power to harm the land and the sea: 3 “Do not harm the land or the sea or the trees until we put a seal on the foreheads of the servants of our God.” Quoting: Revelation 7