Kalru Uchiha

Kalru Uchiha is a demigod, the first of the Uchihas, the creator of Aincrad, and the only known rainbow-type dragon.

History
When Kalru was a mortal elf, before the Spellplague, he fell in love with the evil dragon god, Tiamat. To prove his devotion to her, he allegedly ripped out his own heart to give to her (this heart would later become the artifact known as the Great Ruby of Kalru). Impressed by his devotion, Tiamat revived him and mated with him. This process granted divine power to Kalru, allowing him to take the form of a colossal dragon of no defined color. Along with this, Kalru obtained immortality, and even those who spend time in his presence do not age.

Aincrad
It is unknown if this city was ruled by Kalru before the Spellplague, but it is known that Kalru raised the city up into the sky to avoid the inevitable destruction it would have suffered during the Spellplague. Devastated by the loss of Tiamat, Kalru decided to hide Aincrad away, using his powers to conceal the location of the city until Tiamat returns.

The only way one can access Aincrad is to have the "key" present with them. Zero Uchiha and his group found out that this key is actually Elena Gillil, and that, in fact, the Gillil Clan was created specifically to keep the key safe, as this attribute was passed down to women among the clan for centuries.

Aincrad is currently a city of elves and dragons living harmoniously together.

Personality
Although many Uchiha are known to be at best goal-oriented, ambitious, focused, and at worst, brash, arrogant, and self-centered, Kalru seems to hold little of these qualities himself. He attests the Uchihas inherited these qualities from Tiamat.

Kalru seems to hold little concern for the world outside of Aincrad, showing no interest in leaving or in engaging in the affairs of mortals. Kalru is resigned to waiting for Tiamat, however long it takes, as he is content with his immortality.

What's more, Kalru has even stated if the resurrection of Tiamat was stopped by Zero or anyone else, he would hold them no ill will, believing that the resurrection of Tiamat is inevitable, and though it may take another thousand years, he can wait.