A person who offers himself or herself as a sacrifice (as a religious act, for example).
1728, attributed to Daniel Defoe, The Memoirs of an English Officer, London: E. Symon, p. 186,
After these Street-Exercises, these ostentatious Castigations are over, these Self-sacrificers repair to the great Church, the bloodier the better; there they throw themselves, in a Condition too vile for the Eye of a Female, before the Image of the Virgin Mary […]
A person who is self-sacrificing, who sacrifices their own benefit for the good of another or others.
1856, Amelia M. Murray, Letters from the United States, Cuba and Canada, New York: Putnam, Letter 23, pp. 281-282,
Northern clergymen in Florida, Scotch ministers in the North, and bishops with dioceses each as large as all England; men devoted to religion, charity, and learning—self-sacrificers, fearless, incorruptible […]