I thought it really was founded by those two, and written in Lisp at that. Then YC hooked them up with Swartz and his big thing was rewriting in python. (And maybe there was some contention about this? I forget, but I seem to recall some drama at the time about his contributions.) It was a long time ago, though, so I might be misremembering. In any case, I'm fairly certain Swartz did join after the fact, but I'm not…
> One of the points of the merger was that we would all call ourselves co-founders, so that's what I've been doing. I'd be happy to stop if that's what Steve and Alexis wanted, though.
https://www.reddit.com/r/reddit.com/comments/1octb/reddit_co...
This comment by spez is also interesting https://www.reddit.com/r/todayilearned/comments/d2njs/til_th...
It seems AS was given the title of co-founder by contract, but perhaps, the language was vague enough or they didn't fear retaliation so Steve and Alexis decided they didn't want to acknowledge him as co-founder.
Edit: here are some more details: https://observer.com/2011/07/rumors-acquisitions-did-reddit-... including comments by PG.