Severus Snape, one of the most enigmatic characters in the Harry Potter franchise, has a surprising and significant Patronus - a doe. A Patronus is a magical protector that takes the form of an animal, and Snape's doe symbolizes gentleness and determination. This is unexpected considering Snape's harsh demeanor and villainous role. 

However, his Patronus serves as a reflection of his hidden emotions and unwavering love for Lily Potter, Harry's mother. Lily's Patronus is also a doe, complementing James Potter's stag.

Snape's loyalty, it seems, was not to Lord Voldemort or Dumbledore, but solely to Lily. Despite his complex feelings and relationship with Lily, Snape's Patronus signifies his deep love for her. 

This storyline remains one of the most captivating aspects of the Harry Potter franchise. The significance of Snape's doe Patronus shows that even the most unexpected characters can possess qualities of love and loyalty.