Batman’s got Mr. Freeze and The Flash has Captain Cold, a crazy older dude who likes to freeze stuff as a part of his criminal masterworks. He has a strict sense of morals, despite being a criminal. He refuses to kill women or children, and generally avoids killing ANYBODY except for in special circumstances. He has even teamed up with The Flash from time to time, and is always good or his word when he agrees to a truce. He’s an interesting baddie with many layers, which is probably why he’s generally considered The Flash’s greatest villain.