C.S. Lewis’s wife, the writer Joy Davidman, was named Joy.
Joy Davidman was an American poet and writer who became closely connected with Lewis through their correspondence. The couple married in a civil ceremony in 1956 and later had a Christian marriage ceremony in 1957.
Their relationship became widely known because of Davidman’s illness and death from cancer in 1960. Lewis later wrote A Grief Observed, an intensely personal book responding to bereavement. When it was first published, the book appeared under a pseudonym, a fact that is separate from Davidman’s name.
Davidman was not merely a fictional inspiration or a character created by Lewis. She had her own literary career and published works before meeting him. Her life and relationship with Lewis have also been portrayed in adaptations, but the historical answer to the question is simply Joy.