There are two beasts in Revelation: the beast that comes out of the sea, and the beast that comes out of the earth.
The beast of the sea
The beast of the sea with ten horns and seven heads, of Revelation 13:1-2 and 17:3-10, represents the kingdoms of men.
And I saw a beast rising out of the sea, with ten horns and seven heads, with ten diadems on its horns and blasphemous names on its heads. And the beast that I saw was like a leopard; its feet were like a bear’s, and its mouth was like a lion’s mouth. And to it the dragon gave his power and his throne and great authority.
This beast is a composite of the four beasts of Daniel 7. The four beasts in Daniel 7 had a total of 10 horns and 7 heads, and they included a lion, bear, leopard and something like a dragon. These four beasts represented four different empires (Babylon, Medo-Persia, Greece and Rome). It seems that the beast of the sea in Revelation 13 is a sum of the four beasts in Daniel 7, and so represents the combined “kingdoms of men”, or all human governments.
The beast from the sea reappears in Revelation 17 where it is ridden by a prostitute who represents the false church. In that chapter, the beast is described as a confederation of nations that will oppose Jesus Christ when he returns to the earth (Rev 17:12-14)
The beast of the earth
There is a second beast in Revelation 13 which comes out of the earth:
Then I saw another beast rising out of the earth. It had two horns like a lamb and it spoke like a dragon. It exercises all the authority of the first beast in its presence, and makes the earth and its inhabitants worship the first beast, whose mortal wound was healed. It performs great signs, even making fire come down from heaven to earth in front of people, and by the signs that it is allowed to work in the presence of the beast it deceives those who dwell on earth, telling them to make an image for the beast that was wounded by the sword and yet lived.
This beast is also known as the “false prophet” (Rev 16:13; 19:20). It appears to represent a religious power acting on behalf of the first beast. Many interpreters have suggested that it is the Holy Roman Empire; others have suggested an Islamic power.