Rabia

Rabia was an Umbrum and the mother of Ira and (presumably) Sombra.

History
Rabia-if it was indeed Rabia-spoke to Sombra through the crystal that served as a gateway to the Shadow Prison. She informed him of his true identity and mission, and then unlocked his Umbrum powers so he could carry it out.

In the guise of a fairy-like Umbrum, Rabia befriended Radiant Hope at some point in the distant past, but after the unicorn brought to the Shadow Prison, her true form was revealed to be a grotesque creature. Rabia was particularly annoyed with Hope over the incident, blaming her for the exposure of her deception. She chased the two mares through the prison as the other Umbrum attempted to ambush them.

Behind the scenes
Rabia first appeared by name in though she may well have been Sombra’s unseen mother to whom he spoke in Fiendship is Magic issue 1. She was the most prominent of the Umbrum, and Sombra seems to have paid heed to her without much protest prior to turning against the Umbrum.

Appearances

 * Fiendship is Magic issue 1
 * My Little Pony: Magic Princess
 * My Little Pony: Magic Princess
 * My Little Pony: Magic Princess