The Stormcast Eternals. The unequivocal "good guys" of the Age of Sigmar world. They're getting a new Battletome soon for the game and Games Workshop is giving you a first look inside, along with some of the new special rules that they'll be bringing to the table.
From the article:
The Era of the Beast is upon us. As Sigmar’s champions strike out across the realms on Dawnbringer Crusades, there’s no better time to muster a resplendent army of Thunderstrike Stormcast Eternals – first seen in the Dominion launch box. The rules in the new battletome are about to make them even more fearsome, and not least because they have dragons now.
The Stormcast Eternals still descend from the skies on bolts of lightning, as they have done since the Realmgate Wars, but new rules give these inspiring warriors the power to rally Cities of Sigmar forces to their cause.
You can represent this in-game by deciding if your army is a Scions of the Storm force – the thunderbolt-riding warriors we all know and love – or a more defensive Stormkeep army.