I've seen others with a hero that is legendary and it looks like a wizard of some sort but I don't see an option to get it. How do you get it? Is it just a lucky grab or is there a specific way to get it? I'm not seeing it anywhere in the hero's altar.
The wizard-looking floating hero is the Spirit Mage, which is a gift hero for purchasing 50k gems (roughly $300).
The Thunder God is a new legendary hero (along with the Serpent Queen) which will be available in a future update.
Sooner or later, there will be a new category of "celestial heroes" that features Spirit Mage, Thunder God, Serpent Queen (aka Naga), and new additions. How about a Jaegar? Got the idea from Pacific Rim.