When creating a character blueprint, the blue arrow (for forward) points down the x-axis. Every static mesh I’ve seen also points down the x-axis… for good reason… the marketplace submission guidelines state this. Therefore, one can assume that UE4 treats the x-axis as the “forward” direction.
So why is it that every skeletal mesh (such as characters) face down the y-axis? In fact, the skeletal mesh editor even encourages this bad practice, as it defaults to viewing your character down the y-axis. So you try and follow the earlier mentioned guidelines and wind up with a character always facing to the right every time you open the skeletal mesh editor. Nobody wants to look at their character’s profile when editing animations, so we bow to the skeletal mesh editor and face our characters down the y-axis.
Then it gets ugly… So your character’s facing down the y-axis to satisfy the draconian skeletal mesh editor. Then you go and drop said character into your character blueprint… and uh oh, he’s facing the wrong way! The character blueprint treats the x-axis as forward… of course! So now you have to rotate him 90 degrees to face the right way.
TL;DR The skeletal mesh editor needs to stop behaving badly, and default to viewing your character meshes down the x-axis instead of the y-axis. Epic… hello… did they just hang up on me?