Which Inca ruler was Pachacuti's father?

Pachacuti’s father was Viracocha Inca.

Viracocha Inca was the eighth ruler in traditional lists of Cusco’s Inca rulers, while Pachacuti became the ninth. Pachacuti was born Cusi Yupanqui and later took the name Pachacuti Inca Yupanqui after rising to power and transforming the Cusco state into the expanding Inca Empire.

Traditional accounts describe Viracocha as abandoning Cusco during the Chanka threat, while his son Cusi Yupanqui organized the defense and defeated the invaders. The victory helped Cusi Yupanqui claim the throne and become Pachacuti.

The succession story is not entirely simple. Inca traditions allowed legitimacy to depend on status, lineage, political support, and achievement rather than straightforward European-style primogeniture. Some historians have therefore questioned aspects of Pachacuti’s traditional parentage, but Viracocha Inca remains the standard canonical answer in quiz and reference contexts.

Pachacuti later launched major expansions and is commonly associated with the development of Machu Picchu.