What is "cangjie"

Cangjie is a legendary figure in ancient China (c. 2650 BC), claimed to be an official historian of the Yellow Emperor and the inventor of Chinese characters. Legend has it that he had four eyes and four pupils, and that when he invented the characters, the deities and ghosts cried and the sky rained millet. He is considered a legendary rather than historical figure, or at least, not considered to be sole inventor of Chinese characters. Cangjie was the eponym for the (c. 220 BCE) Cangjiepian proto-dictionary, the Cangjie method of inputting characters into a computer, and a Martian rock visited by the Mars rover Spirit, and named by the rover team.