I think it's more accurate to say that Onfim was a blip in the veil of history as opposed to someone that appeared and gradually disappeared into the veil of history. All the information we have on Onfim, and the only reason we even know he existed, is contained on 17 strips of birch bark that were preserved in mud after being thrown away in the mid 13th century Novgorod, only to be excavated by archaeologists in the 20th century. We know Onfim was the child's name because he frequently signed and wrote it on the bark, and we understand that he was roughly elementary school aged because the schoolwork he was doodling on was primarily remembering the alphabet and writing biblical passages. We know he had a friend named Daniel because one of his drawings contained contains the message "Greetings from Onfim to Danilo." But besides these birch bark drawings and writings, we have no other evidence of Onfim's existence, much less whom his parents were or their occupation. We have no idea if Onfim lived past childhood, or if his future was a happy or sad one, all we have is a brief look into the mindset of a 13th century child in a single year (if that) of his life and education.

The Onfim as "Larry" thing is just a joke that originated from this r/todayilearned thread: https://www.reddit.com/r/todayilearned/comments/cavfyj/til_about_onfim_a_boy_from_13th_century_novgorod/.

In reality Onfim is just a slavicized version of the Greek name Anthemius, while Larry ultimately derives from the Latin name Laurentius, possibly derived from the Latin name for laurel, "laurus".