Tennen Sosa [Joshinsai] (1705-1751)
如心斎

Tennen Sosa (Joshinsai), 7th generation Iemoto of Omotesenke. He is known as the restorer of chanoyu. As the number of tea practitioners increased in the mid-eighteenth century, chanoyu leaned towards becoming a light accomplishment, and the shichijishiki (seven exercises) were devised as a new way of practising in groups.
One of Joshinsai's students (Yokoi Tansho Tsugadayu) wrote down, what his teacher said about tea. This record - the Sawasho (A Selection of the Talks on the Tea Ceremony) - has inspired Sengai's Chado gokui (the Ultimate Meaning of the Way of Tea).

References:
On Joshinsai as an amateur potter, see: Pitelka, Morgan: Handmade Culture; Raku Potters, Patrons, and tea Practitioners in Japan, Honolulu 2005, p.101.
For Joshinsai's and Kyokosai's signatures, see: Encyclopedia of Signatures and Seals (落款花押大辞典 Rakkan Kao Daijiten), Kyoto 1982, pp. 296 and 299.