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. 

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The famous six-syllable mantra of Chenrezig, Oṃ Ṃani Padme Hūṃ, is ubiquitous in the Himalayas, adorning many rocks, prayer wheels and flags.