Of the ten lepers Jesus healed, the one who came back to thank him was what?

Answer: A Samaritan

Only one returned, praising God at Jesus' feet, and he was a Samaritan; Jesus called him "this foreigner."

“When one of them saw that he was healed, he came back, praising God in a loud voice. He fell facedown at Jesus’ feet in thanksgiving to Him—and he was a Samaritan. “Were not all ten cleansed?” Jesus asked. “Where then are the other nine? Was no one found except this foreigner to return and give glory to God?””— Luke 17:15-18 (BSB)