The unfortunately named Hilarius was a trusted priest under Pope Leo the Great. He was given the task with going east and reading Leo’s letter to heretics telling them that they were in the wrong about Jesus’ divinity and that he had two natures,both human and divine,instead of just a divine nature like monophysitism claimed. Leo’s letter went over like a lead balloon and a violent riot ensued(way to take some criticism guys). Hilarius was chased through the streets until he found a hiding place in the tomb of St.John the apostle. Years later when Hilarius became Pope,he built a special chapel in the Archbasilica of St.John out of thanks to the apostle for saving his life during the riots.
Hilarius was also known for making changes to the Mass to make it easier to follow for new converts,probably leading to some of the earliest examples of hand wringing and complaining that the Church “isn’t what she used to be”.
There’s no record of his personality but I’d like to think that he was probably not the funniest guy to be around,just to make his name ironic for my own amusement.
He gets two feast days(bonus feast day!)on February 28th or November 17th,whichever it is the day you want to be hilarious,or joyful,in celebration of Hilarius.