The two fugitive Faltine; Dormammu and Umar entered the universe known as the Dark Dimension, which was inhabited by sorcerers known as the Mhuruuks. Their ruler Olnar dreamed of returning to the days of warfare and conquest. Umar and Dormammu befriended Olnar and played upon these desires. They showed Olnar how to make conquest of other dimensions and bond them with his own. Olnar greedily subjugated several dimensions and added them to his own domain.
In time, the rogue Faltines led Olnar to shatter the barrier between his dimension and that of the Mindless Ones. The Mindless Ones were a horde of soulless brutes that exist simply to destroy anything that lies in their path. The Mhuruuks were beaten back by the onslaught and many were slain, including Olnar. Dormammu and Umar then slew or exiled any wizards that might oppose them. Then they barred the Mindless Ones behind a great mystical barrier.
This battle weakened Umar, and she became subordinate to her brother. Dormammu ascended the throne as regent and ruler of the Dark Dimension. He re-assumed his Faltinian form of flame, but Umar chose to remain in her human form.
Clea was born of an affair between Prince Orini leader of the Mhuruuks and legitimate heir to the rule of the Dark Dimension, and Umar a Faltine and sister to the then-current ruler Dormammu. Umar was disgusted by her relationship with Orini, and abandoned Clea to be raised by him. Prince Orini kept any and all knowledge of Clea's true origins secret.