I'll have to echo other people here with "one", although it seems to be more...situational? "One does not simply walk into Mordor." works but "One went to the store" sounds stupid. "They" is what I would use in that case, because although it usually implies more than one person it doesn't always need to.
That's why I like Japanese. It tends to be a lot more simple for stuff like that. For referring to he/she ("that person" is a better way of putting it) you have different methods based off of affection or familiarity. "ano kata" is very formal, and you won't hear it often in casual conversation. "ano hito" is more casual and a lot more commonly heard. "yatsu" is informal and comes off as rude. Then there are even more (like koitsu, soitsu and aitsu if you're mean ). I think it's a lot more clean and easier to portray emotion.