Rex The Wonder Dog is one of those characters DC writers love to bring up because he's part of the mainstream continuity. He showed up in Superboy and the Ravers (an appearance he's still trying to live down) and he attended the opening of Guy Gardner's restaurant. However, his beginnings are even weirder than his more modern appearances.
Most of Rex's covers feature him protecting his human friends from other animals. Here's an excellent example:
Rex is swinging from a vine and ninja kicking a mountain lion. Pretty cool, right?
Well, then things began to get weird:
Trust me, you do NOT want to know what his Indian name is.
But wait! There's More!
Let slip the dogs of war, indeed! I think the Russians tried this against the NAZIs.
And then we have this:
Rex fighting Barney during a nuclear holocaust. I'm gonna paint that on the side of my van.