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.