In Christianity, the Holy Spirit (or Holy Ghost) is the Spirit of God. In mainstream Christian beliefs, he is the third person of the Trinity. As part of the Godhead, the Holy Spirit is equal with God the Father and with God the Son.
The Christian theology of the Holy Spirit was the last piece of Trinitarian theology to be fully developed. There is also greater diversity in Christian theology of the Spirit (pneumatology) than there is in the theology of the Son (Christology) or of the Father.
The Holy Spirit is frequently referred to by metaphor and symbol both doctrinally and biblically. Theologically speaking these symbols are a key to understanding of the Holy Spirit and his actions, and are not mere artistic representations. When Christ comes up from the water of his baptism, the Holy Spirit, in the form of a dove, comes down upon him and remains with him.
When Stan is searching for God to return him to life in "The Most Adequate Christmas Ever", he runs into the Holy Spirit in the form of a dove using the restroom.
The Holy Spirit is voiced by John DiMaggio.