Joly is a medical student, like Combeferre, but is far more eccentric. Often overly concerned with the health of himself and his environment, he exercises a bit of obsession. That does not stop him from being a good sport amongst friends. He is one-third of the trifecta that is himself, Bosseut, and Musichetta. He shares a gaiety in spirit but not a brashness had by Courfeyrac or Bahorel. This antithesis makes him more devout and agreeable to simple principles, such as those held and promoted by Combeferre.