Like the 24 elders, the four “living creatures” worship God at his throne (Rev 4:6b-8a). The NIV places these creatures “in the center, around the throne.” This reflects the difficulty of the syntax of this line in Greek. It could mean they are simply in the immediate vicinity of the throne, near the throne.
Most scholars think John’s vision draws on the throne room vision from Ezekiel 1-2. If this is true, then these creatures in Rev 4 are cherubim. In Ezekiel the four creatures are a part of the throne of God, more or less the “wheels” of the Throne-Chariot of God. There are, however, a number of differences between these creatures and Ezekiel 1-2. The four creatures are described as having similar other-worldly features. They are “full of eyes,” or “eyes all around.” This is similar to Ezekiel 1; the cherubim are “wheels within wheels, full of eyes.” But the description is also slightly different; the faces are not quite the same in Revelation.
It is possible the description in Revelation recalls something of Ezekiel, but also may have been influenced by other developments in Jewish thinking about angels. One possibility is that John intended to make a reference to archangels. In the Hebrew Bible, there are no archangels, although Gabriel (Dan 8:16, 9:21, Luke 1:18, 26) and Michael (Dan 12:1, Jude 9) are two specific, named angels given that distinction in later Jewish documents. “Archangel” does appear in Jewish literature, but it is perhaps not the right designation for these angels.
It is possible these many-eyed creatures are apocalyptic “watchers.” In some apocalypses written well before the first century, there is a category of angelic being who are designed by God to “witness” everything (1 Enoch 1:5, Jubilees 4:15; 8:3; 10:5). According to 1 Enoch 6-36, some of these angels came down to earth and taught humans sinful practices (like making war and sorcery, but also medicine and cosmetics, 1 Enoch 8). They also had relations with human women and created “the giants.” Michael and Gabriel (along with Surafel or Uriel, depending on the manuscript of 1 Enoch) “observed carefully from the sky” all of this wickedness and called out to the Most High to judge these angels and to destroy the wickedness they had caused (1 Enoch 9-10). The result, of course, is the flood (and a blockbuster Hollywood film).
The Targum on Ezekiel has an expanded description of the cherubim. In Tg. Ezek. 1:6 the angelic beings face four faces, each of which have four faces, sixteen to each creature, with sixty-four faces in all. This kind of elaboration is also found in 3 Enoch 21:1-3:
R. Ishmael said: The angel Metatron, Prince of the Divine Presence, said to me: There are four creatures facing the four winds. Each single creature would fill the whole world. Each of them has four faces and every single face looks like the sunrise. 2 Each creature has four wings and every single wing would cover the world. 3 Each one of them has faces within faces and wings within wings. The size of a face is 248 faces, and the size of a wing is 365 wings. 4 Each creature is crowned with 2,000 crowns and every crown is like the rainbow; its brightness is as the brightness of the sun’s orb and the rays which shine from each separate crown are as the brightness of the morning star in the east. (P. Alexander, OTP 1: 277)
Each of the four creatures has a different appearance. Only the third is said to have the “face” of a man, but based on Ezekiel 1 it may be that only the face is in mind. A major difference between these four creatures and Ezekiel 1 is that each creature has a different face, while Ezekiel 1 describes four creatures with four faces each. These creatures have wings like the Seraphim of Isaiah 6 and they worship God is a very similar manner as the Seraphim, but other characteristics (such as the faces and eyes, etc.) are similar to Ezekiel.
We can know for certain these creatures lead worship in heaven (Rev 4:6-9; 5:8-9, 19:4) and they appear to be associated with the throne of God. In Rev 6:1-7 they will announce the coming of the four horsemen after each seal is opened, and in 15:7 one of these creatures gives the seven bowls of God’s wrath to the angels who pour them out on the earth (16:1).