Black Crown

The Black Crown (Tibetan: ཞྭ་ནག་, Wylie: zhwa nag) is an important symbol of the Karmapa, the Lama that heads the Karma Kagyu school of Tibetan Buddhism. The crown signifies his power to benefit all sentient beings. A corresponding crown, the Red Crown, is worn by the Shamarpa. The Tai Situpa wears a red crown as well, whereas Goshir Gyaltsab wears an orange crown.

Legend tells that in a previous eon, in a former life as an accomplished yogi, the Karmapa attained the eighth level or bhumi of the bodhisattvas. At this time, 100,000 dakinis (female buddhas) manifested their hair as a crown, and offered it to the Karmapa as a symbol of his accomplishment.

Dusum Khyenpa, the 1st Karmapa, was regarded as an emanation of that yogi and his appearance was predicted by the historical Buddha Shakyamuni in the Samadhiraja Sutra:

A bodhisattva with the lion's roar will appear. He will use the power he achieved in deep meditation to benefit countless beings. By seeing, hearing, touching or thinking of him, they will be led to happiness

The Karmapas were traditionally the teachers of the successive Ming Dynasty Emperors of China. When the 5th Karmapa, Dezhin Shegpa, met the Chinese Emperor Yung Lo, the Emperor, through his devotion and spiritual realization, was able to perceive Karmapa in the Sambhogakaya form of Vajradhara (Tib. Dorje Chang), wearing a black crown on his head. The Karmapa explained to the Emperor that he could see the 'Vajra Crown', the power-field of wisdom-energy that always stays above the Karmapa's head. The emperor offered to have a physical replica made so that others could receive its blessing.

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Wikipedia