What we know as hard fact can be limited to "upper-class Jew, a Roman citizen, from Tarsus. Was not an original member of the Jesus movement, but joined and grew to prominence. Wrote earliest surviving case for Jesus' divinity and advocated salvation through Jesus to all mankind, not just the Jews. Was advocate of the idea that Jesus' Gentile followers did not have to follow Jewish laws. Started writing around 50 CE and stopped writing in the 60s CE."

The stories about him go much further. Famously, it has Paul, upon getting in trouble for blasphemy and inciting a riot in Jerusalem, using his right as a Roman citizen to have his case heard by the Emperor, and the Emperor in question, Nero, executing him ~62 CE (give or take a few years). Paul has something of a rivalry with James, Brother of Jesus, who is the head of the early Christian movement in Jerusalem and who wanted a more Jewish Christianity. Paul, who never personally met Jesus, ends up having his arguments win over those of Jesus' brother and James agrees to the compromise that Gentile Christians don't have to obey any of the Jewish laws except for refraining from eating food blessed in the name of foreign gods, eating blood, and refraining from sexual immorality. Critically, that includes circumcision. Paul's argument that faith in Jesus is a circumcision of the heart that transcends the circumcision of the flesh, in one stroke, makes Christianity a far easier sell to non-Jewish converts, who don't have to worry about the unpleasant specter of adult circumcision.

EDIT: there's significant consensus about the authorship of the epistles of Paul, that seven of the 14 epistles attributed to him are authentic.

(14 is counting Hebrews, which never actually claims to be from Paul but was traditionally ascribed to him. It's one of the ones that is considered not authentic)