Only from Plato, Aristophanes and Xenophon in medieval manuscripts.<quoted text>
Is there evidence of Socrates' existence?
I've never actually looked.
Other than a handful of sayings attributed to him, I'm not very familiar.
I will admit to assuming he existed, but if that's doubtful, please enlighten me.
The surviving manuscripts were written over 1000 years after any of the alleged authors lived.
For more dubious than the Jesus biographies (within 200 years of events).