We are first introduced to Henry Clerval in Chapter Two, who is said to be the one friend that Victor Frankenstein made in his childhood. Note how he is introduced:
Henry Cleveral was the son of a merchant of Geneva. He was a boy of singular talent and fancy. He loved enterprise, hardship, and even danger, for its own sake. He was deeply read in books of chivalry and romance. He composed heroic songs, and began to write many a tale of enchantment and knightly adventure. He tried to make us act plays, and to enter into masquerades, in which the characters were drawn from the heroes of Roncesvalles, of the Round Table of King Arthur, and the chivalrous train who shed their blood to redeem the holy sepulchre from the hands of the infidels.
However, let us not dismiss him as a mere romantic. As the novel progresses, we see again and again that his main function lies in the way that he is juxtaposed to his friend's character. Henry is a man of moderation who is able to balance his emotional and rational involvements. In sharp contrast to Victor, Clerval's aspiration is "to become one among those whose names are recorded in story as the gallant and adventurous benefactors of our species." Note, too, how when Victor flees from his creation, it is Clerval who cares for Victor and protects him, which is of course precisely what Victor was unable to do for his own creation. Clerval is finally killed by the creature as part of his revenge for the way in which his mate was killed by Victor.