Andy Gallagher
Andy Gallagher first met the Winchester brothers when they
were investigating a vision of Sam's, involving a young man who
could control people with the sound of his voice.  And, yes, Andy
could do this.  And he didn't always use his powers for pure
good (he convinced Dean to let him take a joy ride in the Impala
once) but neither did he use his powers for anything
approaching evil.

He's a modern day hippie, living in his van called 'The Warrior
Queen."  He reads philosophy and smokes more pot than
Cheech and Chong, and is fairly happy with his life.  Who the
Winchesters were really after was his twin brother, a brother he
didn't know anything about, having been adopted.

The fact that he had an evil twin brother still freaks him out, but
he loves his powers, and controls them very well, so as not to
hurt other people, unlike his twin.
He was going along fine in his life when he ran
into Zoe, another  special child like himself and
Sam, and felt an instant connection with her.  
And when he heard that psychics of all sorts
were disappearing, he convinced Zoe to hit the
road with him.

Knowing the Winchesters as he does, he
wasn't surprised to get the call from Dean.  
Because if there is trouble, usually Sam and
Dean are right smack in the middle of it.  He
saw this as his chance to be a hero, and stop
himself from being captured on top of that, and
helped Dean take down the facility where Sam
and the other children like them were..

But he found out the hero business isn't one of
those you can do part time, and has stepped
up to the plate in the aftermath.