Dan is a decorated soldier from England that is allied with the Harway Plutocracy. He was formerly a sniper, but he is currently retired. Dan married his wife Anne but due to his occupation, he rarely sees her and with her sudden death, it left Dan with regrets. In the manga, he once encountered Twice H. Pieceman in a battlefield and he remembered his expression and opinions about wars.
He was ordered by the Queen to win the Holy Grail but secretly he wishes to revive his deceased wife.
Dan is an elderly gentleman with pure white hair, and a face weathered with the marks of aging. Despite his aged appearance, he does not seem the slightest bit frail, and rather than the mark of weakness, the way he wears his years is more like the way a tree's rings mark its growth. His scars over the years have become a solid core and tough bark that makes it impossible to see his age as a weakness.
Blackmore is a serious man, who is polite and respectful; he is considered "knightly" by his peers. He chooses to face his opponents in honorable battles and frowns on cowardice. Blackmore can also be very compassionate, shown in his last moments when he speaks of his deceased wife.
Blackmore's interaction with his servant seems to be similar to a father and son as he restrains Archer from using dishonorable tactics from winning against an enemy; this ranges from scolding Archer to using a command seal to punish Archer as an extreme method of restraining him. Despite how the Moon Cell Holy Grail War is labeled a war, and while Blackmore was indeed a veteran sniper back in his days as an army soldier, Blackmore sees it more as a contest which is why he is mainly against Archer's seemly advantageous tactics to win before actually facing his enemies when they actually fight fairly.
He is a very devout man, and protective of the image of the Church even in the virtual world of Seraph where it is only used by Aoko and Touko to perform Alterations. He demands that Shinji leave its premises, claiming that the gates of heaven will remain closed to the unbeliever.
He is prepared to die should orders dictate it. He is a soldier that fights solely out of obligation rather than someone else who fights to win the prize for personal reasons.
Dan is first seen encountering Shinji Matou outside of the Church. He chides Shinji for being too loud and having no dignity or respect, and he refuses to let him remain near the chapel. Claiming that it is a place for quiet reflection, someone like him is not welcome there no matter what god they follow. He had believed that the Japanese were polite, but thinks he must have been misled after encountering Shinji. He later encounters Hakuno during the second week, where it is confirmed that he is their opponent. The first remark he makes is that they're green and lack experience. The fact that they let their opponent's appearance shake their resolve is proof of their inexperience, and their eyes look completely lost to him due to their conflict over the death of Shinji. He tells them that they are beyond hopeless in that state, and that entering a battlefield like that will prove disastrous.
He is an elderly soldier working in service to the Queen of England. His absolute adherence to the chivalry puts him at extreme odds with Archer (who is capable of acting significantly on his own due to his very high rank in Independent Action, to the extent of using a Command Seal to forbid Archer from employing guerrilla tactics against Hakuno Kishinami (which is somewhat ironic, considering Dan was a sniper). Archer, in turn, often complains about Blackmore's so-called chivalrous behavior, calling him a sham of a knight on occasion, and for not understanding that Archer cannot win in a fair fight. Blackmore's ultimate goal is to attain the Holy Grail and use his wish to revive his deceased wife; in defeat, he realizes how selfish and petty this wish is.
Ultimately, when defeated, Blackmore accepts death with dignity and apologizes to Archer for not letting him fight as he wished; Archer, in turn, thanks Blackmore for "letting [him] feel like a hero for once". Blackmore then beseeches Hakuno to attempt to find meaning in the death they must inevitably cause, and to honor the fallen - including him - with victory. The Protagonist can come to look on Blackmore as a kind of father figure, depending on choices made in the game.
Saber notes Dan as a seasoned warrior that will force the Protagonist to hone their crude fighting skills if they wish to survive. Rin considers him someone far above the caliber of Shinji. Due to his time as a soldier, actions such as crawling over a mile or sniping an enemy commander are nothing special for him.