If you are not a Buddhist or are not farmiliar, then this might be a goood place to begin your study. The 1000 Armed Chenreig is connected to the four armed Chenresig of Tibet, also known as Kwan Yin in Chinese Buddhism and Avalokiteswara in India. To know more about the four armed Chenresig, please go here.
Now Chenresig was a real man on earth, but owing to his enlightenment, he became a Bodhisattva. It was said that at one time,he vowed to the Buddhas that unless he could bring all snetient beings on earth to enlightenment. He would explode into a million pieces.
He then went about saving all sentient beings from the six realms of Samsara which is the cycle of birth and death. Finally, he was able to bring all beings out of this cycle, but alas, in a blinking of an eye, samsara was filled with beings again. New beings who had succumbed to desires and emotions like anger, greed and jealousy. Chenresig saw to his great sadness that he would never be able to clear samsara of all beings and in his disappointment, he exploded as he pormised into a thousand pieces.
At that moment, Amitabha Buddha saw what happened. With his powers, he put Lord Chenresig back again so that he could continue to help all beings. But this time, Amitabha Buddha turned the Bodhisatvva Chenresig into a thousand armed and thousand eyed Bodhisatvva with eleven faces. To help him look into every corner of samsara and be able to spread his compassion in a thousand directions. Thus arose the coming of the Great Compassionate Thousand Armed and Eyed Chenresig.
It is said that by reciting his mantra, mortals can experience compassion within themselves and for all others. And with the right motivation, they can be cured of illnesses. Many times, this great Bodhisatvva has proved to be very real and powerful.
Personally, I have heard of a daughter who by chanting the dharani of the Great Compassionate Bodhistvva was able to heal her father of lung cancer.