Question: Emperor Go-Toba was what head of the Imperial Family in Japan?

Context paragraphs:
Emperor Go-Toba: Emperor Go-Toba (後鳥羽天皇 , Go-Toba-tennō ) (August 6, 1180 – March 28, 1239) was the 82nd emperor of Japan, according to the traditional order of succession.  His reign spanned the years from 1183 through 1198.

Emperor of Japan: The Emperor of Japan is the head of the Imperial Family and the traditional head of state of Japan.  According to the 1947 constitution, he is "the symbol of the State and of the unity of the people."  Historically, he is also the highest authority of the Shinto religion as he and his family are said to be the direct descendants of the sun-goddess Amaterasu, and his importance also lies in dealing with heavenly affairs, including Shinto ritual and rites throughout the nation.

Imperial House of France (First French Empire): The Imperial House of France during the First French Empire consisted of the family members of Napoleon, including the House of Bonaparte, who held imperial titles as Emperor, Empress, Imperial Prince or French Prince, and who were in the order of succession to the French imperial throne in accordance with the French constitution of 1804.  According to Title III, Article 9 ("The Imperial Family"), "the members of the imperial family in the order of succession, bear the title of Princes of France ("princes français")" and "the eldest son of the Emperor bears the title Prince Imperial ("prince impérial")."

Kiku-ichimonji: Kiku-ichimonji (菊一文字 ) ("Chrysanthemum-straight line"), also "Kiku-ichimoji," often and somewhat erroneously romanized as "Kikuichi-monji," is a collective name given to the Japanese swords made by the thirteen swordsmiths who were in attendance to the Emperor Go-Toba in 1208.  Each swordsmith was in attendance to the emperor for a month of the Japanese calendar.  The swordsmiths of the Fukuoka School traditionally inscribed only the character "Ichi" (一, "one") on the tang as their signature.  They further received permission to append the Imperial chrysanthemum crest (菊, "kiku") on the tang, thus their swords are known collectively as "Kiku-ichimonji".  Go-Toba was interested in the construction of Japanese swords, and so he summoned these swordsmiths, granting them court rank and title, and asked them to share the secrets of the production of higher-quality swords.

Ōke: The Kyu-Miyake (旧宮家 , literally former Miyake ) , also known as the Old Imperial Family (旧皇族), were branches of the Japanese Imperial Family created from branches of the Fushimi-no-miya house.  All but one of the "ōke" were formed by the descendants of Prince Fushimi Kuniye.  The ōke were stripped of their membership in the Imperial Family by the American Occupation Authorities in October 1947, as part of the abolition of collateral imperial houses.  After that point, only the immediate family of Hirohito and those of his three brothers retained membership in the Imperial Family.  However, unofficial heads of these collateral families still exist for most and are listed herein.

Imperial House of Japan: The Imperial House of Japan (皇室 , kōshitsu ) , also referred to as the Imperial Family, and the Yamato dynasty, comprises those members of the extended family of the reigning Emperor of Japan who undertake official and public duties.  Under the present Constitution of Japan, the Emperor is "the symbol of the State and of the unity of the people".  Other members of the imperial family perform ceremonial and social duties, but have no role in the affairs of government.  The duties as an Emperor are passed down the line to their children and so on.

Princess Sukeko: Princess Sukeko (1147–1216) was a princess and an Empress of Japan.  She was the daughter of Emperor Go-Shirakawa.  Sukeko was the mother-in-law (准母) of Emperor Antoku and Emperor Go-Toba.

Battle of Uji (1221): The third battle at the Uji River was the primary battle of the Jōkyū War in Japan.  Bakufu forces led by Imperial regent Hōjō Yoshitoki sought to enter Kyoto and overthrow Emperor Go-Toba, using Uji and Seta as their gateways.

Shin Kokin Wakashū: The Shin Kokin Wakashū (新古今和歌集 , "New Collection of Poems Ancient and Modern") , also known in abbreviated form as the Shin Kokinshū (新古今集 ) or even conversationally as the Shin Kokin, is the eighth imperial anthology of waka poetry compiled by the Japanese court, beginning with the "Kokin Wakashū" circa 905 and ending with the "Shinshokukokin Wakashū" circa 1439.  The name can be literally translated as "New Collection of Ancient and Modern Poems" and bears an intentional resemblance to that of the first anthology.  Together with the "Man'yōshū" and the "Kokinshū", the "Shin Kokinshū" is widely considered to be one of the three most influential poetic anthologies in Japanese literary history.  It was commissioned in 1201 by the retired emperor Go-Toba (r 1183-1198), who established a new Bureau of Poetry at his Nijō palace with eleven Fellows, headed by Fujiwara no Yoshitsune, for the purpose of conducting poetry contests and compiling the anthology.  Despite its emphasis on contemporary poets, the "Shin Kokinshū" covered a broader range of poetic ages than the "Kokinshū", including ancient poems that the editors of the first anthology had deliberately excluded.  It was officially presented in 1205, on the 300th anniversary of the completion of the "Kokinshū".

Jōkyū War: Jōkyū War (承久の乱 , jōkyū no ran ) , also known as the Jōkyū Disturbance or the Jōkyū Rebellion, was fought in Japan between the forces of Retired Emperor Go-Toba and those of the Hōjō clan, regents of the Kamakura shogunate, whom the retired emperor was trying to overthrow.

Supporting paragraphs: Emperor Go-Toba Emperor of Japan
Answer: Emperor of Japan