We don't talk about Him much. He sort of gets slapped on at the end of a blessing, or honorable mention at the deity awards. Most Christian fantasy authors leave Him out altogether (kudos to Lioness for remembering Him in her Trinity).
Who is this guy? Is He the third wheel of the Godhead? There's God the Father, Jesus the Son, and Holy Spirit the Uncle No One Talks About.
As far as I can tell, He's actually kind of important. From www.biblegateway.com:
I understand that to mean the Holy Spirit is who allows a Christian to know truth as God sees it.
When I accepted Christ as my Lord and Savior, something supernatural happened. The Holy Spirit literally possessed me.
This is where non-believers and even a lot of Christians will roll their eyes, shuffle their feet, and either decry me as a kook and a holy-roller or try to change the topic. Sorry, guys, some things have to be said.
I'm not saying I had convulsions or spoke in Tongues or let poisonous snakes bite me. I am saying something more happened than me just making a decision and choosing to act on it the rest of my life, although that happened, too.
When I accepted Christ, I accepted the whole package. That includes God as my Father, Jesus as my Master, Savior, Redeemer, brother (this list goes on a while, so I'll stop there), and the Holy Spirit as my personal God-interpreter. The Holy Spirit sits inside me and whispers stuff, 'cause He's not a shouter. When a nasty thought comes into my mind, the Spirit nudges me. When I behave badly, the Spirit points it out (and I've found "badly" changes meaning the longer I'm in this marriage).
This interpretation works the other way, too.
The Spirit talks to God for us, filtering our childish ramblings into something God can understand.
I have more to say, but there's stuffing to be made this morning.
Keep the faith.