Clea was born to Prince Orini (son of Olnar, the former ruler of the Dark Dimension) and the Faltine fugitive Umar (sister of the Dreadful Dormammu). Clea's birth was very traumatic to Umar and the experience scarred her, even more, when she learned she had lost the ability to revert to her Faltinian form. She abandoned Clea with Orini and became violent, picking a conflict with her brother. In her weakened state, however, she was defeated by Dormammu and banished to another realm.
Clea grew up unaware of who her mother was and worshipping Dormammu, who her father served loyally.
Conquering Planet Earth was part of Dormammu's plans, and, during one of his attempts, Doctor Strange was asked by the Ancient One to travel to the Dark Dimension and try to stop him. Once there, he was seen by a curious Clea, who decided to follow the "human creature". Impressed by him, she sought to save his life by trying to dissuade him from facing Dormammu, but was unsuccessful, as Strange was ready to give his own life to stop him. Soon, Dormammu imprisoned Clea for her betrayal, planning to punish her after battling Strange. However, during the duel between Strange and Dormammu, the Mindless Ones, that were being kept in check by Dormammu, escaped, forcing Strange and Dormammu to work together to contain the creatures. Now in Strange's debt, Dormammu was forced to comply with his desires to release Clea and not invade Planet Earth.
Sometime later, Clea aided Strange again from afar and was once again imprisoned by Dormammu. He forced her to watch as Strange and his nemesis Baron Mordo fought each other, with Strange taking several blows from his foe, but eventually, the tides turned and Strange got close to defeating Mordo. Afraid his puppet would lose, Dormammu decided to enter the battle himself.
Despite its many challenges, Strange was able to win the fight, but when Dormammu returned to the Dark Dimension, he contacted Strange and made him watch as Clea was banished to another dimension. With time, Clea was rescued and Dormammu was dealt with by Eternity, leaving the Dark Dimension without a ruler.
With Dormammu gone, Umar was released from her long exile and decided to succeed where he had failed, so she too cast Clea to another dimension, in the hopes of luring Strange to defeat him. Strange overcame several of Umar's traps and rescued Clea, but in the end, the Ancient One convinced him that she would only be safe if she were sent to another dimension yet again, making him watch as Clea was sent away from him one more time.
Coincidentally, in this new dimension, Clea ran into none other than the Dreadful Dormammu, but history repeated itself as Strange found a way to reach her and defeated Dormammu.
Finally realizing that Earth was the only safe place for her, Strange helped her get an apartment in New York, so she could start her life anew. However, Clea lost her powers on Earth and began missing the Dark Dimension. Hoping to regain her magic abilities, Clea spent countless hours studying in the Sanctum Sanctorum's library, until Stephen Strange became the new Sorcerer Supreme and invited her to become his official disciple in the mystic arts. The two grew close and she joined him on many of his adventures, even helping the Defenders on a few occasions.
In one of their adventures, Clea's soul was corrupted by the evil Silver Dagger and she was transformed into an energy being with increased magical prowess. She attacked Strange, intending to kill him, but, with the help of Marie Laveau and Spider-Man, Strange was able to free Clea from the evil influence and return her to her normal form.
Still, Clea's love for Stephen appeared to be much stronger than his affection towards her, and, after learning that the people of her native realm wanted her to become the new ruler (after Dormammu had disappeared), she decided to return to the Dark Dimension. In spite of Strange's professions of love and him begging her not to leave, Clea mystically departed, resigning her discipleship in the process.
Back in the Dark Dimension, she joined the rebellion to dethrone Umar and learned she was her mother during the fight. After confronting her father, Clea and Umar battled one-on-one, with Clea emerging triumphant and finally becoming the new ruler of the Dark Dimension. She banished Umar and Orini to another dimension, and asked Stephen to remain as her consort, claiming she needed him, but he turned down her offer, telling her his duties were to Planet Earth and that she had more than proved she had no need for his powers nor his wisdom.
Despite their bitter goodbye, however, Clea and Strange met again rather soon, and Strange confessed he was done trying to move past love and wanted to embrace it. Since they couldn't be legally married (due to Clea's status as an extradimensional being), Strange and Clea began wearing magic rings that were actually only one and were therefore mystically connected for all eternity.
Clea couldn't stay on Earth for long periods of time though, as her home dimension was constantly facing the threat of Dormammu, and, every time, the rebellion was counting on her to restore balance. Clea and Stephen's relationship suffered from all the time they would spend apart, and, during one of Clea's visits to Earth, she stumbled upon Stephen apparently dallying with other women, which broke her heart. The two didn't see each other for a while, but Clea still cared for Stephen and, after his fight against the Empirikul left his power levels significantly decreased, Clea appeared in the Sanctum to suggest that they severed their bond, hoping that doing so would remove some magic burden from Stephen and allow him to tap into his full potential with the little power he had left. She even crafted a magical document that, when torn, would nullify any magical contract, but they ended up using it to tame a monster that was threatening Wong. With that taken care of, Stephen told Clea that he was not ready to annul their marriage and, therefore, the two remained connected, but as friends.
At some point, Stephen saw himself with no alternative but to ask for Mephisto's assistance to save reality. Mephisto agreed to help him, but, in return, Clea would lose any memory of Stephen and their time together. He paid her one final visit and asked her if she thought they could ever be together again, thinking she would say "no". As she said "yes", Stephen was heartbroken, as the deal with Mephisto had already been settled and she started to lose her memory. Shortly after, however, Stephen was killed and all the magic spells he'd cast and deals he'd settled lost their effect, allowing Clea to remember him once again. Together with a Temporal Remnant of Stephen, Clea found Stephen's murderer and even had the chance to say goodbye to her husband, when he was briefly revived. Before being claimed by Death again, Stephen told Clea he was a fool for ever letting her go and left her with the Eye of Agamotto and the Cloak of Levitation, claiming there was no else he could trust.
Clea became the new Sorcerer Supreme of Earth and adopted the last name 'Strange' in honor of Stephen. Then, she asked Wong for help in bringing Stephen back, deciding to cast a spell that would warn her of necromantic activity, on the off chance that he'd return to life by himself. Mere moments after doing so, the spell went off, making Clea believe her husband was coming back already. When she got to the epicenter of activity, however, she found a zombified Thunderstrike instead.
