all of us must have some head cannon on him and I ask what yours. his history, relations with ponies, personality, and talent.
for me.
He is the grandson of Luna, he is a Tsundere, his talents represent his role as Equestria's ambassador

Lost both his parents when he was young, was raised by servants, never interacted with foals his age he wasn't related to, got slapped by Cadence when he asked her to marry him when they were six years old. Is the great defendant of the Alicorn of the stars who died during Discord's initial rampage.

4577810 While I don't give him any particular history beyond "noble birth", I draw off the similarities between his Cutie Mark and Daring Do's to put him in an unusual place.

The way I see it, he is really far more at home tromping around exploring the uncharted wilderness than in Canterlot, but he is tied there by his noble heritage and constantly driven up the wall by high society ponies wanting to use his rank and proximity to the princess to climb the social ladder. He feels trapped by this high birth and feels like he is obligated to at least pretend to be like the other nobles so he does everything he can to play the part of the most obnoxiously stuck up noble as an insult to the rest of them. He also uses this to try to drive off the ponies aspiring to trap him one way or another and especially to get out of the formal events he hates by acting like the ponies throwing them are beneath his notice whenever possible.

He lets this persona drop when he is behind closed doors with ponies he trusts, although that is a very short list limited mostly to Celestia and his servants. He is open and friendly around them and does his best to help those he cares about with their problems, although they do often have to listen to him complaining about the other nobles he is forced to deal with. He also has an extensive library of adventure stories, wildlife reference guides, maps, and other works related to his talents which he reads to help relax and learn more about the world beyond the bounds of pony civilization.

Because his real interests run towards adventuring, he makes frequent excursions to the Everfree Forest where he can be himself and explore without having to worry about public perception. This naturally brought him into contact with Zecora who he befriended over their shared interests and eventually fell in love with, although he keeps the relationship secret to protect her from the media and his public image.

For work, I imagine Celestia has him in charge of cartography or something that is more or less in line with his interests, although he still much prefers to be out in the field than any office so there is really no such thing as a good position for him.

4577810 There are a number of headcannons out there. Hell, I read one where he was the son of Sombra who was the brother of The Two Sisters.

Personally, I like to think that Blueblood used to be a caring, giving and happy individual. Celestia got guardianship after both of his parents died when he was a colt. Unfortunately, as the saying goes, 'If you don't learn from history, you are doomed to repeat it.' She didn't pay Blueblood that much attention once Twilight became her student. No matter what accomplishment he achieved, he couldn't match up to Twilight as far as knowledge, magic, or organization. Because of this, he learned how to be a royal by other nobles. Now, he is a rude, obnoxious, womanizer. He figured if his aunt wasn't going to give him attention for his achievements, then she'll give it to him for his antics and attitude...unfortunately, it worked.