So, it'll seem pretty unlikely, and it's possibly non-canon anyway but I've been thinking of a few ways on how the Chosen One could be the Courier. So first off, if Fallout 2 is set 80 years after Fallout 1 (and depending on the age of the Vault Dweller) we got possibly pit their ages to be something like this; Vault Dweller (30-36) Chosen One (20-26) This gives the Vault Dweller some time to have a wife (or partner), have a child who will then have a child of their own. This then leads to the events of new Vegas (which are set 39 years after F2) where the Chosen One will be about 59-65 (unless he was a bit younger in Fallout 2 meaning you can at a stretch put forth the Courier being 58 or 57). It's not too far of a stretch for a 60 year old to be running about and destroying robots and stuff (maybe it's a bit too much of he was around the late 60's or so). This now brings me on to what can be considered the inconsistencies. So why wouldn't anyone recognize the Courier as the Chosen one? Well, aged has made them unrecognizable (this is especially true for Marcus). And the Courier themselves probably can't remember much due to being shot in the head. This could explain why the Courier knows so much of the surrounding areas (and why he has a Vault 13 jumpsuit if you have the DLC installed). The only thing I can think of that negates all of this is Marcus's ending in Fallout 2, where it states that The Chosen One never saw Marcus again. While I don't believe this myself to be the case, I like to think of them as two different entities (maybe the Chosen One and the Courier crossed paths at some point), but it was just a theory I had that people might find interesting.