William Fatianga Marsters (26 November 1923 – 26 August 2004) was the first president of the Cook Islands Christian Church (CICC), the largest religious denomination in the Cook Islands.
He is one of the 134 grandchildren of William Marsters, the English explorer who settled on the then-uninhabited Palmerston in 1863 with his three Polynesian wives.
Bill Marsters became the president of the CICC in 1968, when it was granted autonomy by an Act of the Parliament of the Cook Islands.
He was a popular figure throughout the Cook Islands and administered the church from Rarotonga.
After his resignation, he returned to live in Palmerston Island, where he acted as the CICC pastor and the de facto head of the small island community of Marsters descendants.