Another Pope from a humble background! Jacques d'Euse was in fact also the son of a cobbler; he studied medicine and law, and then rose quickly through the ranks of the church. He had an astonishingly long reign as pope, from 1316 until 1334.

He spent most of it mucking about in European politics, but he's also known for a major controversy that revolves around the 'Beatific Vision.' John XXII said that dead Christians were not immediately admitted to Heaven, but had to wait until the Last Judgement. It might sound innocuous to Protestants, but this would also imply that supplication to saints is useless - if they're, you know, still dead. He held this position during his whole papacy, but never went so far as to make it official doctrine. His successor rescinded it nearly immediately.