In Mary Shelley's Frankenstein, Victor characterizes both Elizabeth and Clerval by contrasting them with himself.

In chapter two, Victor characterizes Elizabeth by setting her against himself.

Elizabeth was of a calmer and more concentrated disposition; but, with all my ardour, I was capable of a more intense application and was more deeply smitten with the thirst for knowledge.

This shows Elizabeth to be far more concerned with the nature of the world over the science of the world. This idea is supported by the following.

While my companion contemplated with a serious and satisfied spirit the magnificent appearances of things, I delighted in investigating their causes.

Therefore, Victor contrasts Elizabeth's love for the natural with his own love for science. This, therefore, sets Elizabeth as a foil to Victor given her love of the natural exists as a polar opposite of science.

Henry Clerval is much like Elizabeth. This again sets Clerval in contrast to Victor.

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.

Here, Victor shows Clerval's love of adventure and fantasy. Here though, one can see a link between Clerval and Victor--they both love creation. Contrastingly, Clerval loves to create stories of fantasy while Victor's desire to create lies in actual creation of a being.

Essentially, Victor sets to describe both Elizabeth and Clerval as being opposites of himself. While both Elizabeth and Clerval love the romantic side of life, Victor finds more pleasure in the scientific aspects of life. Therefore, Elizabeth and Clerval seem to love what could be, Victor loves what he can make happen.

This question is especially interesting because Frankenstein’s supporting cast is so often forgotten in favor of attention toward the great brute. Now, there’s a personality/character/identity study!

In the novel, the reader spends a great deal of the time in either Victor Frankenstein’s or the monster’s head. And not only is one immersed in their subjective worlds, but what comes through the Romanticism of the text is Frankenstein’s and his nemesis’s hardwired constitutions. Elizabeth—her expository passage says she is “of a calmer disposition,” which generally squares with the typical image of what a dutiful Victorian daughter should be. Yet, their Alpine home is no tame Victorian garden: she’s a proto-feminist striver and, in some broader way, an Elemental. She’s set up as perhaps not the emotional core, in comparison to the monster, but the outlet for the author’s, Mary Shelley’s, spirit: Elizabeth is in touch with the wild forces of nature and possesses much the same fervor as that which compelled the author’s own literate expression.

“Dark, gloomy” settings are an important factor in gothic literature, the more wild-blown the better. So, chapter 2 begins with character introductions, but also by painting the setting as a backdrop of gothic dimensions and preoccupations: intensity of feeling, or drive and poetic emotion. Victor mentions “The turbulence of our Alpine summers.” And by Victor"s narrative description, Elizabeth is, essentially, his opposite—in terms of his investigative zeal—not to mention in terms of the dormant psychic “violence” in his nature. He has a doppelganger: a symbiotic, evil twin, yes, but Elizabeth is his opposite within an emotional pair-bond.

Henry Clerval, in his description (returning to my observation about how Shelley’s sensationalistic prose matches the tone and tenor of gothic literature) is a man in his prime, wishing to become “as the gallant and adventurous benefactors of our species,” with no less a role model than King Arthur, and with the esprit de corps of the Round Table. He provides that optimistic, British-Empire manliness and grit.

To get back to Victor, however, a doomed Romantic seeker, he’s the manic catalyst of the destructive plot. When things go wrong in the gothic novels (Frankenstein was first published in 1818), everything goes straight to the devil. A gothic novel is a scandalous tale told in graphic detail: shock effect would be very much the point. One example of foreshadowing in the early section of the novel is the difference between the rapture of Victor's thoughts prior to the creation scene and after. Victor's narrative flights cover extreme contrasts of beauty and revulsion. And, in terms of contrasts in behavior, Henry is Victor’s counterweight. Nonetheless, Victor Frankenstein is isolated from the humanity of his friends and his creation.

Early in the novel, as Victor describes his childhood and young adulthood, he also provides characterization for Elizabeth and Henry Clerval.  Elizabeth does not understand Victor's hunger for science and discovery.  She is more of an Idealist.  She sees the good in others and maintains an optimistic view of humans and the world around her (until Justine's execution).

Henry is the true Romantic.  He enjoys reading romances of old featuring knights and damsels in distress.  When he does go to the university, he chooses to study language so that he can visit and work in exotic locations.  His manner of encouraging Victor is to commune with nature, another primary element of Romanticism.

Victor is, at first, a Meta-physicist.  He believes in the supernatural connection between this world and what cannot be seen.  As he develops, some of his beliefs weaken.  By the end of the novel, one could argue that Victor becomes somewhat of an Existentialist.  He is disillusioned with life and science and thinks of his imagination as a curse.  He is self-centered and feels like "a solitary figure adrift on the open-sea."