The most powerful Planeswalker on Dominaria before the end of the Phyrexian invasion. (Apocalypse was the last set of Magic: The Gathering
cards before Wizards of the Coast
started a new storyline.)
The Argavian calender starts with the date of Urza's birth.
Frequently refered to as 'Urza Planeswalker', he has had an effect on everyone in Dominaria's lives.
For more information.. Read the Magic: the Gathering novels, starting with the first of four books of the Artifact Cycle, "The Brothers' War"
"There were worse things than death, certainly, And so far, Urza Planeswalker seemed capable of them all."