Who is the spirit of truth?

John 15:26 (King James Version)26But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me: John 16:13 (King James Version)13Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come.

The Holy Spirit is the spirit of truth - primarily because He was and is the one sent to teach about the one who is Himself 'the way, the truth and the life.' John 14:6.