Eighth Sapa Inca; son of Yáhuar Huácac. The vision-of-Viracocha episode at Susurpuquio and the subsequent regnal-name adoption represent the most explicit divine-legitimization narrative in the pre-imperial chronicle tradition: a Sapa Inca who took his regnal name from a personal vision of the creator-deity. The Chanka invasion of c. 1438 is the foundational succession-pivot of the Inca empire — Viracocha Inca's flight (with the designated heir Inca Urco) and his son Cusi Yupanqui's defense of Cuzco and acclamation as Sapa Inca produced the dynastic break that inaugurated the imperial period under Pachacuti. The competing Sarmiento and Betanzos accounts of the succession (Sarmiento privileging Pachacuti's legitimacy through Chanka victory; Betanzos drawing on his Inca-princess wife's panaca-internal tradition for a more ambivalent account) preserve the political stakes of the dynastic narrative. Conventional dating: reign c. 1410-1438; death likely c. 1450s in retirement.