An army's gotta have a leader. Otherwise, you just have an unruly mob. A highly-armed unruly mob. Way at the head of the Sigmaran army is the Celestant-Prime. This figure is now available to order from Games Workshop.
Wielding the hammer of Sigmar, Ghal Maraz, the Celestant-Prime hovers his way into battle, looking to turn the tide of Chaos and bring order and good back to the planes.
To go along with him, you can also pre-order the Thunderhead Brotherhood, which is made up of various other Sigmar units all in one bundle.