“there was a form that had the appearance of a man.” The Hebrew words “fire” and “man” are very similar, but “man” fits the context and is properly preserved in the Septuagint. At some point the Hebrew text was improperly transmitted, which is why versions such as the KJV read “fire” and not “man.”
This mysterious figure is not specifically identified in this context, but the evidence in the text is that it is Yahweh Himself. A number of things support this. One of them is that this description of Yahweh is extremely similar to the description of Yahweh in Ezekiel 1:26-27. Also, the form of the man on the throne on top of the platform above the cherubim in Ezekiel 1:26-27 is described as being “the God of Israel” (Ezek. 10:20). Yahweh does appear as a man or man-like figure many times in the Bible (cp. Adam and Eve who heard His footsteps, Gen. 3:8; Abraham, Gen. 12:7; 15:1; 17:1; 18:1; Jacob, Gen. 28:13; Moses and the elders of Israel, Exod. 24:9-11; Samuel, (1 Sam. 3:10; Solomon (twice), 1 Kings 3:5; 9:2; 11:9; Micaiah, 1 Kings 22:19-22; Isaiah, Isa. 6:1-5; Ezekiel, (Ezek. 1:26-28; Daniel, Dan. 7:9-14; Amos, Amos 7:7; Stephen, Acts 7:56; and the Apostle John, Rev. 5:1-8. See commentary on Gen. 18:1).
Also, this spirit uses the first person, “I” or “me” when God is speaking, e.g., Ezekiel 8:6, 17. Also, this “man” refers to the Temple as “my sanctuary” (Ezek. 8:6). Also, the last verse in the chapter, Ezekiel 8:18, is similar to what God had said elsewhere (cp. Ezek. 5:11; 7:9). Also, the Spirit continues speaking in chapter 9, and commands spirit beings in their roles in the destruction of Jerusalem, and by 9:4 the speaker is Yahweh (Ezek. 9:1-4). Then in Ezek. 9:5 the speaker is again referred to as “he,” and Ezekiel identifies him with Yahweh, saying, “Oh, Lord Yahweh!” (Ezek. 9:8). Chapter 9 ends with a statement that is similar to many other places in the Old Testament where Yahweh says He will not spare but will punish people for their sins, and in the closing verse the angel scribe reports back to Yahweh that he has done as “you have commanded me.” The personal appearance of God is theologically referred to as a theophany.