Spoiler — from the ending. Tap to reveal.
“My master... It shall be done, as you command.”
2 quotes from Hellsing Ultimate, each with commentary on what it means and why it stuck.
“My master... It shall be done, as you command.”
“I fear... I must disobey you. Farewell, Integra.”
Earlier, Alucard accepts Integra's order to destroy their enemies; here he vanishes after she commands him to stay. The same relationship reaches the limit of what obedience can accomplish. His apology is more affecting than another pledge would be because it admits that her authority cannot hold him in place. A servant's formality becomes the only courtesy left when service itself is impossible.
Integra has ordered Alucard to leave none of their foes alive on the island. His courteous acceptance gives that violence a chain of responsibility. The reply does not make him a neutral instrument: he accepts the work. Nor does his monstrous capacity absolve the person who commissions it. This is obedience with two accountable participants, not a convenient way to place all the horror inside the vampire.