Which saint used a shamrock to explain the Holy Trinity?

Saint Patrick is traditionally said to have used a shamrock to explain the Holy Trinity.

According to Irish tradition, Patrick held up the shamrock’s three leaves to illustrate the Christian teaching that God is one being in three persons: the Father, the Son, and the Holy Spirit. The plant’s three-part structure made it a memorable teaching symbol during Patrick’s missionary work in Ireland.

Patrick was a fifth-century Romano-British missionary and bishop who is traditionally called the “Apostle of Ireland.” His own surviving writings describe captivity in Ireland, religious conversion, and his later return as a Christian missionary. The shamrock story, however, appears in much later sources rather than in Patrick’s own works.

The earliest written version of the shamrock-and-Trinity legend dates to 1726. That delay does not make the tradition meaningless, but it means historians distinguish Patrick’s documented biography from later stories about him. Another popular legend says Patrick banished snakes from Ireland, although Ireland had no native snakes after the last Ice Age.