Don Diego de Castro Titu Kusi Yupanki (Spanish: [ˈdjeɣo ðe ˈkastɾo ˈtitu ˈkusi ʝuˈpaŋki]; Quechua: Titu Kusi Yupanki [ˈtɪtʊ ˈkʊsɪ jʊˈpæŋkɪ]) (1529 – 1571) was an Inca ruler of Vilcabamba and the penultimate leader of the Neo-Inca State.

After negotiations escalated, around 1568, Titu Cusi was baptized into the Roman Catholic Church, as Diego de Castro.

[1]: xiv, 14–15 Titu Cusi made Túpac Amaru a priest and custodian of Manco Inca's body in Vilcabamba.

The section that describes the moment when Manco Inca, the father of the author and the brother of Atahualpa, receives the first news of the Spaniards' arrival from coastal tribesman is of particular note.

Moreover, we have witnessed with our own eyes that they talk to white cloths by themselves and that they call some of us by our names without having been informed by anyone and only looking into the sheets, which they hold in front of them... Who could people of this manner and fortune be but Viracochas?"