Which Byzantine emperor built the Hagia Sophia?

Justinian I built the Hagia Sophia that stands today in Istanbul.

Construction of the present basilica began in 532, after the previous church on the site was destroyed during the Nika riots in Constantinople. Justinian commissioned the mathematician and engineer Anthemius of Tralles and the geometer Isidore of Miletus to design the enormous domed church. It was completed and dedicated in 537, although earthquake damage later required major repairs and reconstruction.

Hagia Sophia means “Holy Wisdom.” For centuries it served as the cathedral of Constantinople and the principal church of the Byzantine Empire. Its vast dome, supported by pendentives, was a major engineering achievement and made the building one of the defining monuments of Byzantine architecture.

The question refers to the current sixth-century structure, not the earlier churches that occupied the same site. After Constantinople fell in 1453, the building became a mosque. It was a museum from 1935 until 2020, when it was redesignated as a mosque.