Om mani padme hum mantra of six syllables in Sanskrit particularly associated with the four-armed form Shadakshari Avalokiteshvara (Chenrezig Tibetan, Chinese Guanyin), the bodhisattva of compassion.

https://en.wikipedia.org/wiki/Om_mani_padme_hum

History
The mantra originated in India, brought from India to Tibet, the pronunciation changed because some of the sounds of Sanskrit language was difficult for Tibetans to pronounce.