There are many different Buddha aspects and bodhisattvas, but none so famous as Avalokiteśvara (or Chenrezig སྤྱན་རས་གཟིགས་ in Tibetan).
He (or she – Guānyīn in Chinese Buddhism) embodies enlightened compassion.
In his most popular form he appears with four arms showing that compassion has four aspects: loving kindness as an attitude towards all sentient beings; active compassion to alleviate suffering; sympathetic joy to rejoice in the happiness of others; and impartiality, never excluding anyone from the wish for happiness.
These four aspects are called the divine abodes.
The famous six-syllable mantra of Chenrezig, Oṃ Ṃani Padme Hūṃ, is ubiquitous in the Himalayas, adorning many rocks, prayer wheels and flags.