Haile Selassie I (Ge'ez: ቀዳማዊ ኀይለ ሥላሴ Qädamawi Ḫäylä Śəllase, lit. 'Power of the Trinity'; born Tafari Makonnen; 23 July 1892 – 27 August 1975) was the Emperor of Ethiopia from 1930 to 1974. He rose to power as the Regent Plenipotentiary of Ethiopia (Enderase) under Empress Zewditu between 1916 and 1930. Widely considered to be a defining figure in modern Ethiopian history, he is accorded divine importance in Rastafari, a relatively new Abrahamic religion that emerged in the Colony of Jamaica in the 1930s. A few years before he began his reign over the Ethiopian Empire, Selassie defeated Ethiopian army commander Ras Gugsa Welle Bitul, who was the nephew of Empress Taytu Betul, during the Battle of Anchem. He belonged to the Solomonic dynasty, which was founded by Emperor Yekuno Amlak in 1270; Amlak's successors claimed that he was a lineal descendant of Menelik I, the legendary Emperor of Ethiopia who was supposedly born to King Solomon and Queen Makeda of the Kingdom of Israel and the Kingdom of Sheba, respectively. Modern historians regard the Solomonic linage claim as an unfounded myth created by Yekuno Amlak to justify wresting power from the Zagwe Dynasty.

Selassie attempted to modernise Ethiopia by introducing a series of political and social reforms, including the 1931 constitution and the abolition of slavery. He led the failed effort to defend Ethiopia during the Second Italo-Ethiopian War and was consequently exiled in the United Kingdom after the beginning of the Italian occupation of East Africa. In 1940, he travelled to Anglo-Egyptian Sudan to assist in coordinating the Ethiopian struggle against Fascist Italy, and was able to return home following the East African campaign of World War II. He later dissolved the Federation of Ethiopia and Eritrea, which was established by the United Nations General Assembly in 1950, and annexed Eritrea as one of Ethiopia's provinces, while also fighting to prevent Eritrean secession.

As an internationalist, Selassie led Ethiopia's accession to the United Nations as a charter member. In 1963, he presided over the formation of the Organisation of African Unity, the precursor of the African Union, and served as the institution's first chairman. By the early 1960s, many prominent African socialists, such as Kwame Nkrumah, Ahmed Sékou Touré, and Ahmed Ben Bella, envisioned the creation of a "United States of Africa" to rival the similar concept of a federal Europe. The rhetoric of this faction, especially in light of the then-ongoing Cold War, was overwhelmingly anti-Western, and Selassie saw this as a threat to the alliance he had so calculably constructed. Therefore, he took it upon himself to attempt to influence a more moderate posture within the group.

Amidst popular uprisings by the country's students, peasants, urban dwellers, merchants, political activists, and marginalised religious and ethnic groups, Selassie was overthrown by the Derg in the 1974 Ethiopian coup d'état. With support from the Soviet Union, the Derg began governing Ethiopia as a Marxist–Leninist state. In 1994, three years after the fall of the Derg military junta, it was revealed to the public that the Derg had assassinated Selassie at the Jubilee Palace in Addis Ababa on 27 August 1975. On 5 November 2000, his excavated remains were buried at the Holy Trinity Cathedral of Addis Ababa.

Among some adherents of Rastafari, Selassie is referred to as the returned Jesus—that is, the Messiah and God incarnate. This distinction notwithstanding, he was a Christian and adhered to the tenets and liturgy of the Ethiopian Orthodox Church. He has been criticised by some historians for his suppression of rebellions among the landed aristocracy (Mesafint), which consistently opposed his changes. Some have also criticised Ethiopia's failure to modernise rapidly enough. During his reign, the Harari people were persecuted and many left the Harari Region. His administration was also criticised by human rights groups, such as Human Rights Watch, as autocratic and illiberal. According to some sources, late into Selassie's administration, the Oromo language was banned from education, public speaking and use in administration, though there was never an official law or government policy that criminalised any language. His government also relocated many Amhara people into southern Ethiopia, where they served in government administration, courts, and church. Following the death of Ethiopian civil rights activist Hachalu Hundessa in 2020, the Bust of Haile Selassie in the United Kingdom was destroyed by Oromo-speaking protesters, and an equestrian monument depicting his father Makonnen Wolde Mikael was also removed from Harar.