Born during Scotland's high middle ages, Diam was thrown into a world of political conflict and steel. This quickly molded him into something he may not have agreed with being, but something he came to accept nonetheless. His kind, at the time, was few. This left him with little choice in how he could live his life in such a world, finding work was near impossible and finding a safe home even more so.
Instead, he chose to live on the move, hopping from village to city to hamlet to hovel in hopes of finding something worth staying with. Of course this never came. He was destined to never have a home, he believed.
Around 1150AD, Diam decided to put his skill with a blade to proper use and become a self-proclaimed lawman, wandering the lands around him and bringing swift and bloody justice to those who sought to bring terror and fear to those who couldn't fight for themselves. At first, he was just as ruthless as those he cut down. Over time, however, he came see that he was bringing just as much fear as they. This sparked a change in him that motivated him to become less brash and reliant on his blade, becoming less of a show-off, as it were.
His choice of lifestyle shaped his personality dramatically. Over time, he found it harder to trust the people around him. This left him with difficulty forming new relationships and maintaining existing ones. This difficulty in itself made him slightly withdrawn from society, causing him to mostly avoid social interaction when possible, but did not make him entirely unwilling to interact. Should the mood strike, he can be just as social, playful and as open as the next person. Just don't expect him to spill his guts any time soon.