What kind of relationship does Barry have with this Captain Cold fellow? He's often mentioned in conjunction with Flash.
Captain Cold is often the de facto leader of the Rogues, a group of Flash villains. Originally, he forms the group when he and the other villains realize they don't stand a chance against the Flash alone. Over time, they become a surrogate family to one another. The whole thing is that they are a band of thieves with a code of honor. Cold and his boys are not insane or want to take over the world like other villains; they're blue collar types who just want to make money and get on with their lives. They watch each other's backs and have a no kill policy; they'll flat out abandon a job if it puts innocent lives in danger. They won't even kill the Flash, despite knowing that they could do it with a team effort.
I haven't read much Flash stuff, but I love the Rogues in everything I've seen them in and they're a big reason I'm excited for this show.