was the 12th emperor of Japan, according to the traditional order of succession. Historians consider Emperor Keikō to be a legendary person; and the name Keikō-tennō was created for him posthumously by later generations.

No certain dates can be assigned to this emperor's life or reign.  The conventionally accepted names and sequence of the early emperors were not to be confirmed as "traditional" until the reign of Emperor Kammu, who was the 50th monarch of the Yamato dynasty.

Traditional history
Keikō is almost certainly a legend; but the Kojiki and Nihonshoki record his name.

Events of Keikō's life
The limited information about Keikō does not imply that no such person ever existed. Very little information is available for study prior to the reign of the 29th monarch, Emperor Kimmei. 

In Kojiki, Keikō sent his one of his sons to Kyūshū to fight battles on his behalf. In Nihonshoki, Keikō fought and won these battles against local tribes. According to both sources, he sent Yamatotakeru to Izumo province and eastern provinces to expand his territory.

After his death 
This emperor's official name after his death (his posthumous name) was regularized many centuries after the lifetime which was ascribed to Keikō.

The actual site of his grave is not known.  According to the Imperial Household Agency, this emperor is venerated at a memorial Shinto shrine (misasagi) at Nara.  The kami of  Emperor Keikō is also venerated at Anaho jinja in Anaho, Ōmi province.

Spouses and children
Empress (first): Harima no Inabi no Ooiratsume (播磨稲日大郎姫), daughter of Wakatakehiko (若建吉備津日子)
Prince Kushitsunowake (櫛角別王)
Prince Oousu (大碓皇子), ancestor of Mugetsu no kimi (身毛津君)
Prince Ousu (小碓尊), father of Emperor Chūai

Empress (second): Yasakairihime (八坂入媛命), daughter of Yasakairihiko (八坂入彦命)
Prince Wakatarashihiko (稚足彦尊) Emperor Seimu
Prince Iokiirihiko (五百城入彦皇子)
Prince Oshinowake (忍之別皇子)
Prince Wakayamatoneko (稚倭根子皇子)
Prince Oosuwake (大酢別皇子)
Princess Nunoshinohime (渟熨斗皇女)
Princess Iokiirihime (五百城入姫皇女)
Princess Kagoyorihime (麛依姫皇女)
Prince Isakiirihiko (五十狭城入彦皇子), ancestor of Mitsukai no Muraji (御使連)
Prince Kibinoehiko (吉備兄彦皇子)
Princess Takagiirihime (高城入姫皇女)
Princess Otohime (弟姫皇女)

Mizuhanoiratume (水歯郎媛), daughter of iwatsukuwake (磐衝別命), younger sister of Iwakiwake (石城別王)
Princess Ionono (五百野皇女) Saiō

Ikawahime (五十河媛)
Prince Kamukushi (神櫛皇子), ancestor of Sanuki no Kimi (讃岐公), Sakabe no Kimi (酒部公)
Prince Inaseirihiko (稲背入彦皇子), ancestor of Saeki no Atai (佐伯直), Harima no Atai (播磨直)

Abe no Takadahime (阿倍高田媛), daughter of Abe no Kogoto (阿倍木事)
Prince Takekunikoriwake (武国凝別皇子)

Himuka no Kaminagaootane (日向髪長大田根)
Prince Himuka no Sotsuhiko (日向襲津彦皇子)

Sonotakehime (襲武媛)
Prince Kunichiwake (国乳別皇子)
Prince Kunisewake (国背別皇子)
Prince Toyotowake (豊戸別皇子)

Himuka no Mihakashihime (日向御刀媛)
Prince Toyokuniwake (豊国別皇子), ancestor of Himuka no Kuni no miyatsuko (日向国造)

Inabinowakairatsume (伊那毘若郎女), daughter of Wakatakehiko, younger sister of Harima no Inabi no Ooiratsume
Prince Mawaka (真若王)
Prince Hikohitoooe (彦人大兄命)

Igotohime (五十琴姫命),　daughter of Mononobe no Igui (物部胆咋宿禰)
Prince Igotohiko (五十功彦命)

Related pages
 Emperor of Japan
 List of emperors of Japan
 Japanese imperial family tree

References

Other websites
 Keikō's misasagi -- map 

Emperors of Japan