As nouns the difference between altruism and martyr
is that altruism
is regard for others, both natural and moral without regard for oneself; devotion to the interests of others; brotherly kindness; selflessness; contrasted with egoism or selfishness
is one who willingly accepts being put to death for adhering openly to one's religious beliefs; notably, saints canonized after martyrdom.
As a verb martyr is
to make someone into a martyr
by putting him or her to death for adhering to, or acting in accordance with, some belief, especially religious; to sacrifice on account of faith or profession.