What's the noun for altruists? Here's the word you're looking for.
altruism
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.
(biology) Action or behaviour that benefits another or others at some cost to the performer.
“Misguided though this might have been, my grandfather was motivated by altruism and a deep belief in human dignity.”
“When it comes to moral action, we must act in silence, in much the same way that Wittgenstein acted himself when he helped others in his life of altruism and self-chosen poverty.”
“One can't help but suspect that the motive behind the Italian researcher's efforts is rooted in gaining glory and renown rather than altruism.”