Khelgar Ironfist is a dwarven fighter and the first major companion the player encounters. He is a fighting fanatic, and as such is heading to Neverwinter to learn to become a Monk after being impressed by two monks who beat him senseless despite their appearing weak. He has to pass a series of tests to become eligible to be a monk after which he can be releveled from level 1 up as a monk. He also has a storyline where he must reconcile with his clan after they resent him for his putting his love of fighting before the clan. After the events of the game, he is believed to be dead, however, it is not true.
In the best ending of Mask of the Betrayer, if the player was in a romance with either Safiya or Gann, then Khelgar, along with Neeshka, attend their wedding.
He appears again in Storm of Zehir expansion, as a temporary ruler of Crossroad Keep and a member of Neverwinter Nine. He is waiting for the Knight-Captain (the Player Character) to return.
Source: Wikipedia, "List of Neverwinter Nights characters", available under the CC-BY-SA License.