John Thomas Mateer (born December 4, 1995), also known as Johnny Saint Marks, is an American musician, filmmaker, and entertainment entrepreneur. He grew up in Wantagh, New York. Mateer was an early-era content creator on YouTube in the late 2000s, and his first media appearances resulted from the viral content that he created on the platform. Shifting his focus towards music at the beginning of the 2010s, Mateer released his first extended play, Love is Not a Lifestyle, in the summer of 2011. Mateer's entrepreneurial endeavors include the founding and operation of the post-production company, RIOT MOTION LLC and the nonprofit organization, Empathy Always Corp, which provides relief to victims of narcissistic abuse. Mateer also writes screenplays and poetry, his first published collection of poetry, The Flight of a Monarch: Poetry From Young Adulthood, was released in spring 2023.