fallout-4
Is the player character in Fallout 4 a synth?
The game doesn't answers this question directly, as far as I know.
It would feel kinda like it makes sense, the Institute making Synths and you
as a Synth becoming the new leader of the Institute.
Is the player character in Fallout 4 a Synth? What evidence exists (either in-game or comments of developers) that support the answer?
Progress with the main story quest to get ahead with the Brotherhood of Steel. Before that, you can only repeat Rhys' and Haylen's quests over and over.
[Possible Spoiler] When does the next quest appear?
Near the end of the quest Reunions (credit to DCShannon)
Redditor RandomVigilante made a nice (if possibly not 100% accurate) map of coverage.
You might want to check out the full Reddit Thread for more information on this map (including flaws, and possibly a Red/Green Colorblind friendly version).
Best Answer
In the Automatron DLC quest, Restoring Order, when you gain access to The Mechanist's lair, over the speaker you hear "incoming robot detected, opening security doors" (you have a robot with you during this quest) but then you hear "no bio signs detected, proceed".
That is the biggest piece of evidence I have seen to support the main character being a synth. The character was scanned and there were no traces of bio life. I didn't want to believe I was a synth either but that really opened my eyes to the idea. Hard proof.