Aragorn- Aragorn is the son of Arathorn and descendant of Isildur who didn’t cast the One Ring into the fires of Mount Doom when he should have. Aragorn is the rightful King of Gondor, the White City. He is the main human in the trilogy and part of the Fellowship of the Ring.
Boromir and Faramir- These are the children of “King” Denethor of Gondor. Boromir is an arrogant man who is good at heart but easily tempted. Boromir is deceased. Boromir died for the noble cause of taking as many orcs as possible to protect Frodo as he was part of the Fellowship of the Ring. Faramir was sent into an unwinnable battle. He was wounded severely but was saved by Peregrin Took and went on to love Eowyn, daughter of Theoden.
Gandalf (sorta): Gandalf is a sort of exception. While he is a Spirit who lives for just about ever, he was sent in the time of need in Middle-Earth in the form of a man. He is always saving those in need during the adventures. Gandalf was part of the Fellowship of the Ring.
Sauron (sorta): Sauron is the main antagonist and is very powerful. He is more powerful than Gandalf and super evil. He lives in Mordor to the North, and created the rings. 5 rings to the dwarves, 3 to elves, 9 to men and one for himself.
I did not know all of this, so please check out my references.