That’s the hero Doug (Infantry), and you can get him this weekend in Doug’s Challenge event (ONLY 12 hours left). Just kill 40 monsters and trade in the event items to summon him.
At 5-stars, Doug will give you 30% chance of doubling your rewards when used to kill monsters, dragons and tribes. This includes speed ups, player experience points, summoning tickets (from dragons), equipment, resources and hero levelling tomes.
It’s recommended to save all your universal purple hero fragments and use it get him to at least 3-stars by the end of the event on Sunday. Use all your mobility potions today.
Even if you don’t plan to use him, you can sell all your fragments for 100 gems apiece.
If you end up short on fragments, or miss the event. No worries it will come back around in a few weeks.
Don’t forget to check out the “Event” icon on the top right. Follow the quests in each event to pick up all the goodies.