Basil had an almost epic stroke of luck. He was really a nobody; a textbook example of the rags to riches story.
He started out as just a party-hardy friend of Michael II. Moreover, he was illiterate and lacking in any connections inside the military, nobility or the Byzantine religious system. While it's unclear what initial relationship the two had for one reason or another they became friends. Michael himself was a weak ruler who was only too happy to delegate his responsibilities to underlings to have a good time in the palace. In time, he came to appreciate Basil enough to bestow on him the highest imperial title and make him his equal to the amazement of everyone.
After his coronation Basil became a good and responsible leader, again to everyone's surprise. But this irritated Michael who felt upstaged and especially resentful that his protege was no longer just his drinking pal but an emperor telling him to clean up his act. When Basil saw the writing on the wall he noticed that nothing good would come out of this partnership in the long run and arranged to have Michael assassinated in a pre-emptive move.
Basil went on to successfully deal with the usual threats to the empire on all points of the compass while continuing a program of economic restoration and also started an ambitious project to overhaul the legal code.
He died on what was presumably a hunting accident and the throne passed to Leo VI.
SB 1702, DOC III 1 AU Solidus Obv: +IhSXPSRXRGNANTIM - Basil I wearing loros, holding globe with patriarchal cross and akakia.
Rev: +bASILIOSCθbASILVSb - Constantine and Eudocia. December 867 - January 868 (Constantinople).
SB 1708 AR Miliaresion Obv: IhSSXRISVShIC - Cross potent on three steps; globe beneath.
Rev: +bASI/LIOSC/COhSAh/IhSPISV/bASILIS/ROMOS - Inscription in six lines. (Constantinople).
SB 1709, DOC III 12 Follis Obv: +bASILIOSbASILEVS* - Basil enthroned facing, holding labarum.
Rev: +bASILIOSENQEObASILEVSROMEON - Legend in four lines. 867-886 (Constantinople).