structural:summarization
Pachacuti Inca Yupanqui, also called Pachacútec (Quechua: Pachakutiy Inka Yupanki), was the ninth Sapa Inca of the Chiefdom of Cusco, which he transformed into the Inca Empire (Quechua: Tawantinsuyu). Most archaeologists now believe that the famous Inca site of Machu Picchu was built as an estate for Pachacuti.

In Quechua, the cosmogonical concept of Pachakutiy means 'the turn of the world' and Yupanki could mean 'honorable lord'. During his reign, Cusco grew from a hamlet into an empire that could compete with, and eventually overtake, the Chimú empire on the northern coast. He began an era of conquest that, within three generations, expanded the Inca dominion from the valley of Cusco to a sizeable part of western South America. According to the Inca chronicler Garcilaso de la Vega, Pachacuti created the Inti Raymi to celebrate the new year in the Andes of the Southern Hemisphere. Pachacuti is often linked to the origin and expansion of the Inti Sun Cult.

Accessing power following the Inca-Chanka war, Pachacuti conquered territories around Lake Titicaca and Lake Poopó in the south, parts of the eastern slopes of the Andes Mountains near the Amazon rainforest in the east, lands up to the Quito basin in the north, and lands from Tumbes to possibly the coastal regions from Nazca and Camaná to Tarapacá. These conquests were achieved with the help of many military commanders, and they initiated Inca imperial expansion in the Andes.

Pachacuti is considered by some anthropologists to be the first historical emperor of the Incas, and by others to be a mythological and cosmological representation of the beginning of the era of Inca imperial expansion.