Formally called 内閣総理大臣 naikaku sôri daijin ("general minister of the cabinet"): informally called 首相 shushô (lit. "neck of the council"). Japan's prime minister (premier) is elected by the Diet and serves as the country's head of government. The first prime minister was elected by the first Diet following the signing of the Meiji Constitution, and although the office has gone through many functional changes since then, it has essentially remained the same. Prime ministers live in the Kantei in Nagata-cho, and get to fly around in a Boeing 747 strangely remniscient of Air Force One.
Before the Allied occupation of Japan, prime ministers were not elected by the Diet: they were appointed, first by a body called the genro, and during the early days of the Showa era, by the ruling military junta. Partisan politics therefore did not really begin until the late 1940's. Those prime ministers that were affiliated with parties are denoted by the following abbreviations:
D = Minshuto (Democratic Party of Japan)
DK = Doshikai (Comrades' Assembly)
K = Komeito (Public Light Party)
KC = Kakushin Club (Innovation Club)
KI = Kyokoku Itchi (National Unanimity)
KK = Kokumin Kyodoto (Citizens' Cooperative Party)
KS = Kenseito and Kenseikai (Constitutional Government Party/Assembly)
L = Jiyuto (Liberal Party)
LDP = Jiminto (Liberal Democratic Party)
MS = Minseito (Civil Government Party)
NJ = Nippon Shinto (New Japan Party)
NS = Shinto Sakigake (New Party Sakigake)
P = Shinpoto (Progressive Party)
S = Shakaito (Japan Socialist Party/Social Democratic Party of Japan)
SS = Shinseito (New Life Party)
SY = Seiyukai (Friends of Government Assembly)
Most Japanese political parties are extremely short-lived: only the Liberal Democrats have had any extended reign of political power, and today only half a dozen parties are represented in the Diet.
Note that, as in most parliamentary systems, the premiers of Japan have no term limits or fixed election cycle, so their periods of rule can seem rather random, but tend to reflect the political direction of Japan at the time. Those marked as "provisional" were not elected, but assumed office temporarily following the death of the previous premier: some lists will include them, while others won't. Prince Sanjo is also often left out of official lists.
Names are written in Japanese style with the family name first.
Meiji Era (Emperor Meiji)
Name From To Home Party
Count Ito Hirobumi 1885 1888 Choshu
Kuroda Kiyotaka 1888 1889 Satsuma
Prince Sanjo Sanetomi 1889 (concurrent with Kuroda for two months)
Prince Yamagata Aritomo 1889 1891 Choshu
Prince Matsukata Masayoshi 1891 1892 Satsuma
Count Ito Hirobumi 1892 1896 Choshu
Kuroda Kiyotaka 1889 (provisional)
Prince Matsukata Masayoshi 1896 1898 Satsuma
Count Ito Hirobumi 1898 Choshu
Okuma Shigenobu 1898 Saga KS
Prince Yamagata Aritomo 1898 1900 Choshu KS
Count Ito Hirobumi 1900 1901 Choshu SY
Saionji Kimmochi 1901 (provisional)
General Katsura Taro 1901 1906 Choshu
Saionji Kimmochi 1906 1908 Kyoto SY
General Katsura Taro 1908 1911 Choshu
Saionji Kimmochi 1911 1912 Kyoto SY
Taisho Era (Emperor Taisho)
General Katsura Taro 1912 1913 Choshu
Yamamoto Gombei 1913 1914 Satsuma SY
Okuma Shigenobu 1914 1916 Saga DK
Terauchi Masatake 1916 1918 Choshu
Hara Takashi (Hara Kei) 1918 1921 Iwate SY
Uchida Yasuya 1921 (provisional)
Takahashi Korekiyo 1921 1922 Tokyo SY
Admiral Kato Tomosaburo 1922 1923 Hiroshima SY
Uchida Yasuya 1923 (provisional)
Yamamoto Gombei 1923 1924 Satsuma KC
Kiyoura Keigo 1924 1924 Kumamoto SY
Showa Era (Emperor Showa aka Hirohito)
Kato Takaaki 1924 1926 Aichi KS
Wakatsuki Reijiro 1926 1927 Shimane KS
Tanaka Giichi 1927 1929 Yamaguchi SY
Hamaguchi Osachi 1929 1931 Kochi MS
Wakatsuki Reijiro 1931 Shimane MS
Inukai Tsuyoshi 1931 1932 Okayama SY
Takahashi Korekiyo 1932 (provisional)
Saito Makoto 1932 1934 Iwate KI
Okada Keisuke 1934 1936 Fukui KI
Baron Hirota Koki 1936 1937 Fukuoka KI
Hayashi Senjuro 1937 Ishikawa
Prince Konoe Fumimaro 1937 1939 Tokyo KI
Hiranuma Kiichiro 1939 Okayama
General Abe Nobuyuki 1939 1940 Ishikawa
Admiral Yonai Mitsumasa 1940 Iwate
Prince Konoe Fumimaro 1940 1941 Tokyo
General Tojo Hideki 1941 1944 Tokyo
General Koiso Kuniaki 1944 1945 Tochigi
Admiral Suzuki Kantaro 1945 Osaka
Prince Higashikuni Naruhiko 1945 Tokyo
Shidehara Kijuro 1945 1946 Osaka
Yoshida Shigeru 1946 1947 Tokyo L, P
Katayama Tetsu 1947 1948 Wakayama S, D, KK
Ashida Hitoshi 1948 Kyoto D, S, KK
Yoshida Shigeru 1948 1954 Tokyo L, D
Hatoyama Ichiro 1954 1956 Tokyo LDP
Ishibashi Tanzan 1956 1957 Tokyo LDP
Kishi Nobusuke 1957 1960 Tokyo LDP
Ikeda Hayato 1960 1964 Hiroshima LDP
Sato Eisaku 1964 1972 Yamaguchi LDP
Tanaka Kakuei 1972 1974 Niigata LDP
Miki Takeo 1974 1976 Tokushima LDP
Fukuda Takeo 1976 1978 Gumma LDP
Ohira Masayoshi 1978 1980 Kagawa LDP
Ito Masayoshi 1980 (provisional)
Suzuki Zenko 1980 1982 Iwate LDP
Nakasone Yasuhiro 1982 1987 Gumma LDP
Takeshita Noboru 1987 1989 Shimane LDP
Heisei Era (Emperor Akihito)
Uno Sosuke 1989 Shiga LDP
Kaifu Toshiki 1989 1991 Aichi LDP
Miyazawa Kiichi 1991 1993 Hiroshima LDP
Hosokawa Morihiro 1993 1994 Kumamoto NJ, S, SS, K, D, NS
Hata Tsutomu 1994 Nagano SS, NJ, D, K, L
Murayama Tomiichi 1994 1996 Oita S, LDP, NS
Hashimoto Ryutaro 1996 1998 Okayama LDP, S, NS
Obuchi Keizo 1998 2000 Gumma LDP, L
Mori Yoshiro 2000 2001 Ishikawa LDP
Koizumi Junichiro 2001 2006 Kanagawa LDP
Abe Shinzo 2006 2007 Yamaguchi LDP
Fukuda Yasuo 2007 2008 Gunma LDP
Taro Aso 2008 ---- Fukuoka LDP