The man who became Frank, enslaved by the Williams family, was born in 1661 on the coast of West Africa. He was named Quashi after the day of his birth, a Sunday. Quashi was of the Bullom people, also known as the Sherbro, who still live in the area, which is today part of the country of Sierra Leone.
You can learn more about Frank on the Raid on Deerfield website.