Emperor Tenmu (also romanized Temmu, c. 630 – 686) was 40th Emperor of Japan according to the traditional order of succession. He was born Prince Ōama around 630, the son of Emperor Jomei and his consort Princess Takara. Ruling from 673 to 686, during the Asuka period, his life is mainly documented by the chronicles Nihon Shoki and Kojiki, as well as the poetry collection Man'yōshū.

Little is known of Ōama's early life. During the rule of his elder brother Tenji, Ōama was ambiguously favored as his successor, but was gradually bypassed in favor of Tenji's son Prince Ōtomo. Tenji allegedly offered Ōama the throne during an illness in 671, but fearing a conspiracy against him, Ōama declined and left to serve as a monk at Yoshino Palace. Tenji died soon after. The following year, Ōama received word that Ōtomo, now ruler, was planning to kill him. He fled Yoshino with a group of followers, beginning the Jinshin War. Along with a group of retainers and the governor of Ise Province, Ōama was able to block off the mountain passes to the northern and eastern provinces, where he raised an army against his nephew. Ōtomo was defeated and forced to commit suicide. Ōama took the throne under the name Tenmu.

Tenmu made a number of political reforms, modeling his government after the centralized state of Tang China. He was likely the first Japanese ruler to use the title of tennō ('emperor') and the first to be described as a divine being (kami) in his lifetime. He redistributed political titles among his family and political supporters and created four new ranks at the top of the kabane noble title system. He selected a site for a new capital around 683, on which (after his death) was likely built Fujiwara-kyō. He was an enthusiastic supporter of both Buddhism and the goddess Amaterasu, making various reforms to Buddhist clerical governance and elevating Amaterasu's Ise Shrine to preeminence in Japan.

Tenmu's health began to decline in 685. In attempt to gain divine favor, the imperial court sponsored large-scale Buddhist rituals, but he died in 686. This began a mourning period and interregnum almost twice the length as usual, during which both of his crown princes died: Prince Ōtsu was executed later the same year, likely on the orders of Tenmu's consort Uno-no-sarara, while Prince Kusakabe died of ill health in 689. Uno-no-sarara ascended to the throne in 689 as Empress Jitō.

Prince Ōama was the son of Emperor Jomei of Asuka Japan and his consort Princess Takara, and the younger brother of Naka no Ōe. His date of birth is unclear; traditional sources date his birth to either 613 or 621, but this would make him older than Naka, born in 626. Some modern historians have estimated a date around 630, owing to the existence of a middle sister, Princess Hashihito, between the two brothers. Due to the much older date in traditional sources, archaeologist Yuji Seki theorized that Ōama may have been the son of Takara and her first husband, Prince Takamuku.

Jomei had ascended to the throne in 629, around the time of Ōama's birth, following the death of the long-reigning Empress Suiko. Suiko had never selected an heir after the death of Prince Shōtoku in 622, leading to a protracted succession dispute between Jomei (the grandson of Suiko and Emperor Bidatsu) and Shōtoku's son Yamashiro. Although Jomei took the throne with the support of Senior Minister Soga no Emishi, Yamashiro continued to press his claim.

Upon Jomei's death in 641, Yamashiro stood as the strongest potential candidate for emperor, as Jomei's crown prince Naka no Ōe was only sixteen years old. However, Emishi continued to oppose Yamashiro, and proposed Jomei's son Furuhito no Ōe (whose mother was a member of the Soga clan) take the throne. Lacking significant backing, Emishi agreed to a compromise following the precedent of Empress Suiko's ascension, and Princess Takara took the throne as Empress Kōgyoku. Emishi's son Soga no Iruka became the dominant political figure during Kōgyoku's reign, seizing control of administrative affairs and purging many of his opponents, including Yamashiro and his family. A triumvirate of three statesmen—Nakatomi no Kamatari, Soga no Ishikawa Maro, and Prince Naka no Ōe—assassinated Iruka in 645. Kōgyoku abdicated, initially intending for Naka to take the throne; however, with pressure from Nakatomi, her brother Prince Karu took the throne as Emperor Kōtoku.

Kotoku was succeeded by the former Empress Kōgyoku in 655, who reigned again under the new name Saimei. In 660, the Korean kingdom of Baekje (an ally of Japan) fell to a combined Tang–Silla force. The following year, Saimei, alongside Naka and Ōama, sailed to Kyushu to oversee the construction of an armada to invade Korea and restore Baekje. Saimei died in Kyushu in the 9th month of that year, and Prince Naka was appointed as an interim regent, unwilling to officially take the throne; two years later, the Japanese armada was defeated. Naka oversaw the expansion of fortifications around Kyushu, seeking to defend against a possible Sino-Korean invasion, and integrated provincial elites into the court rank system. These efforts increased royal authority, but created considerable unrest among the Japanese clans.