The aim of this paper is to investigate the origin and meaning of the unique New Testament pneumatological terms “Comforter” (Παράκλητος) and “Spirit of truth” (πνεῦμα τῆς ἀληθείας), which are found only in the Gospel of John and which are of great theological importance for understanding the pneumatology of the early Church. In the attached paper, we will attempt, based on the text of the Gospel itself, but also on other extra-biblical testimonies in which the terms Παράκλητος and πνεῦμα τῆς ἀληθείας are mentioned, to come to a conclusion about the origin of the terms themselves, that is, about the possible sources that served the writer in using them, and then to analytically present their meaning and sense, as understood and presented by Saint John the Theologian in his Gospel.