I think of the fictional character Dr. Sylvester Ashling, the child psychologist with sleep-related powers, from the web series Epithet Erased. He is often called by the nickname Sylvie.
Sylvester Pussycat first appeared as a character in 1939, but was not given a name until 1948. The name Sylvester was chosen because "Felis silvestis" is the scientific name of the European wildcat, which is the closet wild relative of the domestic cat.
Sylvester Graham (1794–1851) was an American minister often in the USA referred to as the 'father of vegetarianism' whose preaching inspired the invention of the earliest of modern cereals, and the naming of graham flour products such as the graham cracker.