I thought to go a bit against stereotype, especially because of finding the very useful trait Overlooked Mastermind.
For those that don't know:
Source Inner Sea Races pg. 212
Some half-orcs use half-orcs’ brutish stereotypes to their advantage, causing others to underestimate their intelligence and scheming. Such half-orcs gain a +2 racial bonus on Bluff, Diplomacy, and Sense Motive checks. This bonus increases to +4 against other humanoids. They also receive a +2 racial bonus on Bluff checks to feign ignorance and Sense Motive checks to intercept secret messages, and this stacks with the above bonus. This racial trait replaces intimidating, orc ferocity, and weapon familiarity.
Personally I feel this single trait is worth its weight in gold, as the expression goes, and think that it could be used to created a very interesting yet effective character. Especially if I play up on the idea that most would think half-orc are unintelligent, brutish, and oafs that are too dim to be insightful, cunning, or deceitful.
Any ideas on how to strengthen the idea, even perhaps create an orc who can be the social face of the party and that uses the views others might have of him being a half-orc to his advantage? Ways to really bring out the fun and even create perhaps a very potent manipulator style character?
I was considering adding the Skilled trait as well, though I felt that wasn't as much a focus. Your half-orc thinking he was an human child of an Orc blooded Sorcerer was an interesting idea, was he also a sorcerer?
A mesmerist actually isn't a bad idea at that, and their character does seem to be an interesting build. That is a good though as well, especially if one wants to go more sneaky. More, a mesmerist is a pretty sweet class in general, one of my favorites of the occult classes. Especially as a fan of illusions, enchantment, and general manipulative characters.
Any other ideas?
While that trait goes well with bard mechanically, since you are wanting to play up the stereotypes to your own advantage, I don't think that that really meshes with bard all that well, as bards are showy, and while you could normally roleplay that sort of name based connotation on a class away, the showy-ness of bards is heavily tied to the mechanics of the class (what with bardic performances and versatile performances) so it would be difficult to maintain such a charade for any length of time if you need to use your class abilities or use any of the instrument based performances and thus carry around an instrument, because the savvy npcs (and thus the ones that it actually matters to fool) are going to see those and see "bard" instead of "brute."
I second the mesmerist idea if you want to go the spell castery route, otherwise I would recommend rogue, especially with a str and cha focused rogue, probably the skulking stalker half-orc archetype or whatever it's called, use a big, ugly two hander that you can carry around strapped to your back to further sell the illusion.
All in all, I really like the idea, and it kind of makes me think of how almost nobody in the marvel comics looks at the incredible hulk (even post split with banner) and sees a genius physicist, even though he is. However, your bard idea makes me think of the indelible krunk (or whatever he was called) from the Dexter's Lab shorts but with Van Halen's (or whatever he was called) axe, if that was how it was, I can totally imagine people seeing that and thinking of him as a charismatic rock star (ie, bard) and not necessarily big, dumb brute, which is what it sounds like you're going for, in terms of public perception.
Hope this helps!
Another consideration perhaps, with your last paragraph, being that of the Skald and even that of the archetype Fated Campaign. Of the this and the bard, the former would better fit the "rock star" motif while also still allowing him to be very intelligent and amiable. At least it is an idea, I am open for any others people may have.