1853, "unselfishness, devotion to the welfare of others, opposite of egoism," from French altruisme, coined or popularized 1830 by French philosopher Auguste Comte, with -ism + autrui (Old French altrui) "of or to others," from Latin alteri, dative of alter "other" (see alter). The -l- is perhaps an etymological reinsertion from the Latin word.
There is a fable that when the badger had been stung all over by bees, a bear consoled him by a rhapsodic account of how he himself had just breakfasted on their honey. The badger replied peevishly, "The stings are in my flesh, and the sweetness is on your muzzle." The bear, it is said, was surprised at the badger's want of altruism. ["George Eliot," "Theophrastus Such," 1879]