Pope Telesphorus
Earlier in his life he worked with the hermits of Mount Carmel in Palestine and is still remembered in the Carmelite Order of Monks.  He is credited with the custom of the Midnight Mass, celebrated at Christmas and for the period of reflection during the season of Lent but this is disputed.  He celebrated Easter on Sundays whereas many early Catholics were observing the Jewish custom and celebrating it on Passover.