The Holy Trinity with Saint John the Baptist and Saint Sebastian (early 16th Century) in the Manner of Timoteo Viti - Public Domain Catholic Painting

The Christian doctrine of the Trinity defines God as being one god existing in three coequal, coeternal, consubstantial persons: God the Father, God the Son and God the Holy Spirit — three distinct persons sharing one essence. In this context, the three persons define who God is, while the one essence defines what God is. Source

John the Baptist was an itinerant preacher active in the area of the Jordan River in the early 1st century AD. Source

Saint Sebastian was an early Christian saint and martyr. According to traditional belief, he was killed during the Roman emperor Diocletian's persecution of Christians. He was initially tied to a post or tree and shot with arrows, though this did not kill him. Source