Originally the Aspect of Earth, Neltharion the Earthwarder became corrupted by the whispers of the Old Gods, transforming into Deathwing.
Alexstrasza is the Aspect of Life, and also the Dragonqueen.
Ysera is the Aspect of Nature. She was an adoptive mother to Cenarius, and watches over the Emerald Dream.
Nozdormu is the Aspect of Time. He watches over (presumably) all of the timelines. It is known that in one(or perhaps several) he is corrupted and becomes Murozond, the leader of the Infinite Dragonflight.
Malygos was the original Aspect of Magic. He saw it unfit that mortals commanded magic the way they did, and attempted to kill them off, but ultimately died in the process of attempting such.
Kalecgos was originally a simple blue dragon. He assisted in battling the Burning Legion at the Isle of Quel'Danas, and later became the Aspect of Magic through a special ritual.