What is "sosei"

Sosei (, 844 – 910) was a Japanese waka poet and Buddhist priest. He is listed as one of the Thirty-six Poetry Immortals, and one of his poems was included in the famous anthology Hyakunin Isshu. His father Henjō was also a waka poet and monk.

Sosei entered religious life sometime after his father, who took the tonsure after the death of Emperor Ninmyō in 850.