Kaya Alp
Kaya Alp was, according to Ottoman tradition, the son of Kızıl Buğa and the father of Suleyman Shah, who was, in turn, the grandfather of Ertuğrul, and the great grandfather of the Ottoman Empire founder, Osman I.
Abd al-Muttalib
Abd al- Muttalib Shaybah ibn Hashim( c. 497 – 578) was the grandfather of Islamic prophet Muhammad.
Henry Bryant (naturalist)
Henry Bryant( May 12, 1820 – February 2, 1867) was an American physician and naturalist.
He was the grandfather of Henry Bryant Bigelow.
Tankei
Tankei (湛慶 1173 – June 13, 1256) was a Japanese sculptor of the Kei school, which flourished in the Kamakura period.
He was the student of and eldest son of the master sculptor Unkei.
Guillaume Wittouck
Guillaume Wittouck( 1749- 1829) was a Belgian lawyer and High Magistrate.
He was the Grandfather of industrialist Paul Wittouck.
Prithvipati Shah
Prithvipati Shah( ?–1716) was the king of the Gorkha Kingdom in the Indian subcontinent, present- day Nepal.
He was the grandfather of Nara Bhupal Shah.
Fujiwara no Nagara
, also known as Fujiwara no Nagayoshi, was a Japanese statesman, courtier and politician of the early Heian period.
He was the grandfather of Emperor Yōzei.
Lyon Cohen
Lyon Cohen( 1868–1937) was a Polish- born Canadian businessman and a philanthropist.
He was the grandfather of singer/ poet Leonard Cohen.
John Westley
Rev. John Westley( 1636 – 78) was an English nonconformist minister.
He was the grandfather of John Wesley( founder of Methodism).
Unkei
Unkei (c. 1150 – 1223) was a Japanese sculptor of the Kei school, which flourished in the Kamakura period.
He specialized in statues of the Buddha and other important Buddhist figures.
Unkei's early works are fairly traditional, similar in style to pieces by his father, Kōkei.
However, the sculptures he produced for the Tōdai-ji in Nara show a flair for realism different from anything Japan had seen before.
Today, Unkei is the best known of the Kei artists, and many art historians consider him its "most distinguished member".

Question: Who is Tankei's paternal grandfather?
Answer: Kōkei