Anchoring the thread
The Eremites blamed Urizen for "snatching away" the gleaming future they had envisioned for the Homeworld, as the orchestrator of the Anchoring of the Thread — which not only bound the Spiral Politic to an orderly set of laws, but also, in trade-off, made the Houses themselves static and sterile. (PROSE: The Book of the War)
In Eremite art, Urizen was caricatured as a blind old man using a set of dividers to measure his own dung as spittle hung from his lips. Despite their vows of silence, the Eremites celebrated the "rites of Urizen" by laughing freely. (PROSE: The Book of the War)
One member of the Collective of the Retconning Crocodiles once told Auteur that he thought that while the Crew of the Copper-Colored Cupids were "inconsequential fools", their Creator was nevertheless a genius, and when he put it into terms for Auteur, he said that the Creator was the equivalent of "a lovechild of Urizen and Nikola Tesla" if that child had then "pursued a double career in robotics and biodata-manipulation". (PROSE: Resurrection of the Author)
Behind the scenes
Urizen is the embodiment of reason and law in William Blake's mythology. In Blake's designs, Urizen is usually portrayed as a bearded old man carrying either architects' tools to constrain the universe or nets to ensnare people in webs of law. His opponent is the embodiment of imagination, Los. The description of the Eremites' caricatures of Urizen is an apparent parody of Blake's The Ancient of Days.
In any event, identifying a bearded old man, known as an architect and for tying the world down in law, as the first President of the Great Houses of the Time Lords, is obviously reminiscent of Rassilon. Rassilon had been described as an architect and as the originator of the Laws of Time as early as in The Deadly Assassin, and the even more explicitly godlike Matrix Lord incarnation featured in Doctor Who Magazine comics such as The Tides of Time even depicted Rassilon as a bearded old man wearing robes, bringing the character even closer to the Blakean Urizen. In addition, Urizen's antagonism with the embodiment of imagination Los is arguably mirrored by Rassilon's enmity with the Carnival Queen.
However, it is worth noting that not every source places Rassilon as the first President of the Time Lords. According to The Legacy of Gallifrey, the Gallifreyans were already ruled by Presidents even before Rassilon and Omega were born; The Scrolls of Rassilon, meanwhile, states that Pandak was the President of Gallifrey throughout the Eternal War and it was only after becoming a hero of said War that Rassilon overthrew him in a coup. As such, based purely on in-universe evidence, Urizen could plausibly be Pandak or indeed someone else entirely.