From peasant to emperor
Basil was born to peasant parents in late 811 (or sometime in the 830s in the estimation of some scholars) at Charioupolis in the Byzantine theme of Macedonia (an administrative division corresponding to the area of Adrianople in Thrace).
The name of his father is unknown, but the name of his grandfather was Maïktes; his mother was named Pankalo (Παγκαλώ), and her father was called Leo. His ethnic origin is unknown, and has been a subject of debate. During Basil's reign, an elaborate genealogy was produced that purported that his ancestors were not mere peasants, as everyone believed, but descendants of the Arsacid (Arshakuni) kings of Armenia, and also of Constantine the Great. The Armenian historians Samuel of Ani and Stephen of Taron record that he hailed from the village of Thil in Taron. In contrast, Persian writers such as Hamza al-Isfahani, or al-Tabari call both Basil and his mother Saqlabi, an ethnogeographic term that usually denoted the Slavs, but can also be interpreted as a generic term encompassing the inhabitants of the region between Constantinople and Bulgaria. Claims have therefore been made for an Armenian, Slavic, or indeed "Armeno-Slavonic" origin for Basil I. The name of his mother points to a Greek origin on the maternal side. The general scholarly consensus is that Basil's father was "probably" of Armenian origin, and settled in Byzantine Thrace. The author of the only dedicated biography of Basil I in English has concluded that it is impossible to be certain what the ethnic origins of the emperor were, though Basil was definitely reliant on the support of Armenians in prominent positions within the Byzantine Empire.
Basil victorious in a wrestling match against a Bulgarian champion (far left), from the Madrid Skylitzes
One story asserts that he had spent a part of his childhood in captivity in Bulgaria, where his family had, allegedly, been carried off as captives of the Khan Krum (r. 803–814) in 813. Basil lived there until 836, when he and several others escaped to Byzantine-held territory in Thrace. Basil was ultimately lucky enough to enter the service of Theophilitzes, a relative of the Caesar Bardas (the uncle of Emperor Michael III), as a groom. While serving Theophilitzes, he visited the city of Patras, where he gained the favour of Danielis, a wealthy woman who took him into her household and endowed him with a fortune. He also earned the notice of Michael III by his abilities as a horse tamer and in winning a victory over a Bulgarian champion in a wrestling match; he soon became the Byzantine Emperor's companion, confidant, and bodyguard (parakoimomenos).
Symeon Magister describes Basil in fitting terms for a champion wrestler, he was "... most outstanding in bodily form and heavy set; his eyebrows grew together, he had large eyes and a broad chest, and a rather downcast expression".
On Emperor Michael's orders, Basil divorced his wife Maria and married Eudokia Ingerina, Michael's favourite mistress, in around 865. During an expedition against the Arabs, Basil convinced Michael III that his uncle Bardas coveted the Byzantine throne, and subsequently murdered Bardas with Michael's approval on April 21, 866. Basil then became the leading personality at court and was invested in the now vacant dignity of kaisar (caesar), before being crowned co-emperor on May 26, 866. This promotion may have included Basil's adoption by Michael III, himself a much younger man. It was commonly believed that Leo VI, Basil's successor and reputed son, was really the son of Michael. Although Basil seems to have shared this belief (and hated Leo), the subsequent promotion of Basil to caesar and then co-emperor provided the child with a legitimate and Imperial parent and secured his succession to the Byzantine throne. It is notable that when Leo was born, Michael III celebrated the event with public chariot races, whilst he pointedly instructed Basil not to presume on his new position as junior emperor.
When Michael III started to favour another courtier, Basiliskianos, Basil decided that his position was being undermined. Michael threatened to invest Basiliskianos with the Imperial title and this induced Basil to pre-empt events by organizing the assassination of Michael on the night of September 23/24, 867. Michael and Basiliskianos were insensibly drunk following a banquet at the palace of Anthimos when Basil, with a small group of companions (including his father Bardas, brother Marinos, and cousin Ayleon), gained entry. The locks to the chamber doors had been tampered with and the chamberlain had not posted guards; both victims were then put to the sword. On Michael III's death, Basil, as an already acclaimed co-emperor, automatically became the ruling basileus.