In the world of Harry Potter, a wizard and witch's Patronus is important to their identity. Case-in-point, when Harry discovers his Patronus is a stag in The Prisoner of Azkaban, which is similar to his father's Patronus -- a stag -- and his mother's -- a doe. Fans also learned that Severus Snape's Patronus was a doe, showing his love for Lily Potter still remains. However, one Patronus that was not seen is Professor Remus Lupin's, and that's probably because fans didn't need official confirmation to know what it was.
Introduced in Prisoner of Azkaban as a former member of the Marauders and an original member of the Order of the Phoenix, Lupin was the Defence Against the Dark Arts teacher. Despite being arguably the most competent Dark Arts tutor Harry and company ever had, he couldn't remain at the post when it became public knowledge that he was a werewolf, thus it makes too much sense that his Patronus is also a wolf.
As a kid, Lupin was bit by the werewolf Fenrir Greyback and permanently affected with Lycanthropy, turning into a fully-fledged werewolf once a month. He was able to teach at Hogwarts for a year when Snape made him a Wolfsbane potion that helped tame his wolf-self.
Like several classic werewolf stories, the power to transform into a wolf is more a curse than a gift. A person with lycanthropy loses their humanity as they transform into a vicious animal, endangering those closest to them. When turning back into a human, they are remorseful for the violent acts committed out of their control. Despite having a fitting Patronus, Lupin doesn't like that his is a wolf because he hates being a werewolf.
Author J.K. Rowling confirmed Lupin's Patronus on the Wizarding World website, stating he "dislikes the form of his Patronus, which is a constant reminder of his affliction. Everything wolfish disgusts him, and he often produced a non-corporeal Patronus deliberately, especially when others are watching."
However, despite Lupin understandably resenting his Patronus, it also can be viewed as an expression of his positive aspects. Rowling also wrote that, "Wolves are family-oriented and non-aggressive," which are character traits accurate to Lupin when he's not a werewolf.
One of the series' most unlikely but heartwarming love stories is the one between Lupin and Order of the Phoenix member Nymphadora Tonks. Despite their age and wealth gap -- and Lupin's condition -- the two put aside their differences to get married and start a family. Just as Snape's Patronus changed into a doe out of his love for Lily, Tonks' Patronus changed from a jackrabbit to a wolf after falling for Lupin.
While it's unknown how Lupin felt when Tonks Patronus changed into a wolf before their tragic deaths, it hopefully helped change how he viewed his own wolf Patronus. The wolf represents both the bad in him that was not his fault and the good qualities in him. It would also only make sense that their son Teddy Lupin would grow up to have a wolf Patronus as well.