Yu-81 is the number of a legendary prisoner that Shukhov observes over dinner. In many ways, Yu-81 is a picture of Shukhov's possible future, if he stays in the camp. Unlike most of the prisoners, Yu-81 has survived for years with dignity and pride. He refuses to be degraded into an animal-like existence, as we see in his one and only scene:
This was Shukhov's chance to take a close look at him. With hunched-over lags all around, he was straight-backed as could be. He sat tall, as though he'd put something on the bench under him. [...] He was steadily eating his thin skilly, but instead of almost dipping his head in the bowl like the rest of them, he carried his battered wooden spoon up high. (1029)
Shukhov clearly admires this man and the way that he carries himself. And, in certain ways, Shukhov himself is quite similar to Yu-81, particularly in how they behave with dignity.