558i

'' When this universe is gone, I will make a new one in its place. And then I will destroy it too. And then remake it. Entropy at a scale never known before.  - 558i

558i
558i was one of the imaginary numbers that came to Num in the Imaginary Invasion. He came to Num due to the effects of the B E A N collider incident, and then proceded to turn all of the other elite scientists imaginary.

0 + 558i
Due to the Trials of Nullstradamus going on, 558i pretended to be 558, and then succeded in the trials. This allowed him to channel the power of 0, (despite 539's efforts to stop him) to which he used to free the other imaginaries, who were currently stuck in the lab.

0 + 558 + 558i
When it seemed things couldn't get any worse, 0 + 558i was able to take over 558 completely, allowing him to become the all powerful 0 + 558 + 558i. In this form, he was able to easily defeat anyone in his way.

Goals and Motives
558i or 0 + 558i or 0 + 558 + 558i (depending on if you can be bothered to say his full number) had the intent of removing all of reality's laws so that Num wouldn't be limitied anymore, like the other imaginaries. However, his immense complex power caused him to go mad, and then he decided to just destroy this universe, and to remake it. And then repeat. Entropy on a massive scale.