From Lutheran Service Book:
“Early in the fourth century, a north African pastor named Arius began teaching that Jesus Christ was not truly God. The Church responded decisively in AD 325 with a statement of faith (The Nicene Creed), which confessed that Jesus is, in fact, true God. Toward the end of the fifth century, another creed was written that delved further into the mystery of the Trinity. Though attributed to Athanasius, a fourth-century opponent of Arius, this anonymous creed clearly came at a later stage in the debate.
The Athanasian Creed declared that its teachings concerning the Holy Trinity and our Lord’s incarnation are “the catholic faith.” In other words, that is what the true Church of all times and all places has confessed. More than fifteen centuries later, the Church continues to confess this truth, confident that the triune God, Father, Son, and Holy Spirit, has given Himself to our salvation.”