Okay, this is a pretty controversial one, as it usually is when Christian and Jewish ways of interpreting the Bible start to clash. In Chapter 7: 13-14, Daniel says that, in his night visions, "I saw one like a human being coming with the clouds of heaven. And he came to the Ancient One and was presented before him. To him was given dominion and glory and kingship, that all peoples, nations, and languages should serve him. His dominion is an everlasting dominion that shall not pass away, and his kingship is one that shall never be destroyed."
So, first off, quick translation note: the "one like a human being" phrase is very gender-neutral and politically correct. However, not everyone renders the original Hebrew this way. Many translators (and most ancient translators) read this as "one like the Son of Man," which sounds pretty similar in content, but is way different in function.
In the New Testament, "Son of Man" (the New Testament authors weren't known for their progressive non-gendered language) is used as an honorific, denoting someone who simultaneously represents the height of humankind and is a divine messianic figure. For Christian interpreters, it's pretty obvious who the "Son of Man" is, receiving dominion and glory over an unending kingdom and ruling over everyone on earth: J.C. And the phrase "Son of Man" pops up in the gospels of Jesus just about 80 times. They really took to it, apparently.
But Jewish interpretations naturally cut into the idea differently. The "one like a human being" or "one like a Son of Man" could be the Messiah, and a bunch of apocalyptic works written shortly after Daniel love emphasizing this possibility. It could also be the archangel Michael, who's been pretty epically calling the shots and getting stuff done all throughout the book. Some medieval commentators suggested it could also be Israel itself (or the people of Israel) raised up to a position of higher moral authority over the world.
Anyway, those are the traditional religious interpretations. But why is he "like" a human being or Son of Man? Why isn't it just one who "is" a human being or, more simply, a "human being"? Well—that's a tough one. You could read it different ways: perhaps he's one "like" a human being, because he isn't really a human being, but represents something else like the whole of Israel, or an archangel, or God incarnated as a human being, or what have you.
One thing's for sure: in Daniel, whoever this guy is, he's got a serious role to play in the end times and God's divine judgment.