Avalokiteshvara, the Bodhisattva of compassion, in front of Buddha Amitabha made to commitment to intentionally manifest into the three realms of Samsara in order to harrow the depths; that is to say, in order to stir from depths and completely liberate all sentient beings from samsara, and to be their supreme guide.

link: Legend of the 1000 Armed Avalokiteshvara