Karmapa 

The title of the reincarnating head of the Karma-kagyü lineage, the first of whom was Düsum Khyenpa (Dus-gsum mkhyen-pa, 1110-93), who was succeeded by sixteen further incarnations down to the present day. The Karmapa's main role in the lineage is to ensure that the transmission of the school's tantric teachings is passed intact down through the generations. A key element of the installation of a new Karmapa is the use of a black hat said to be woven from the hair of a ḍākinī.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)