Tertullian , a Latin theologian who wrote in the early 3rd century , is credited as being the first to use the Latin words `` Trinity '' , `` person '' and `` substance '' to explain that the Father , Son , and Holy Spirit are `` one in essence -- not one in Person '' .
Tertullian , a Latin theologian who wrote in the early third century , was the first to use `` Trinity '' `` person '' and `` substance '' to explain that the Father , Son and Holy Spirit are `` one in essence -- not one in Person . ''