My dissertation is about Eiko & Koma, who began their dance training with Hijikata in the early 1970s, before going to train with Ohno Kazuo. Some people see Ohno as a co-founder of butoh, others see him as its most visible proponent. He just passed away earlier this summer at the age of 103. I'm not going to try to define butoh for you here - that's a dissertation in itself.
There just aren't very good clips of Hijikata's choreography online, so I'll just include some pictures of him here. Use your imagination!
From the Kamaitachi by Hosoe Eikoh:
Still from History of Smallpox (1972)