"The Tenth Inca, Tupac Inca Yupanqui - He had his dark blue helmet umachuccu, mascapaycha, anaspacra, his champi and uallcanca, and his bluish mantle, and his shirt of tocapa, and four bands around his legs. He was a very elegant man, tall of stature, very wise and friendly. He kept peace and friendship with the great lords, and he liked feasts and banquets. He liked to honour the principal ladies, and he was a very great warrior. He was an enemy of lyers; for a lye he ordered the person to be killed."
(A Manuscript by a Peruvian Indian Poma de Ayala at the Royal Library of Copenhagen).(1)

The maritime adventures of Tupac Inca Yupanqui -

He was not the eldest son but his father picked him because he is a warrior...

His father appointed him to head the Inca army in 1463. He extended the realm northward along the Andes through actual Ecuador, and developed a special fondness for the city of Quito, which he rebuilt with architects from Cuzco. During this time his father Pachacuti reorganized the kingdom of Cuzco into the Tahuantinsuyu, the "four provinces"...

He became Sapa Inca in his turn upon his father's death in 1471, ruling until his own death in 1493. He conquered Chimor, which occupied the northern coast of what is now Peru, the largest remaining rival to the Incas.

Pedro Sarmiento de Gamboa - History of the Incas - Chapter 46:

"Tupac Inca Yupanqui sets out, a second time, by order of his father, to conquer what remained unsubdued in Chinchay-Suyu.

Pachacuti Inca Yupanqui knew from the report made by his son when he returned from the conquest of Chinchay-suyo, that there were other great and rich nations and provinces beyond the furthest point reached by Tupac Inca. That no place might be left to conquer, the Inca ordered his son to return with a view to the subjugation of the parts of Quito. He assembled the troops and gave his son the same two brothers as his colleagues, Tilca Yupanqui and Anqui Yupanqui, who had gone with him on the former expedition...
In this way he arrived at Tumipampa, within the territory of Quito, whose Sinchi, named Pisar Ccapac, was confederated with Pilla-huaso, Sinchi of the provinces and size of Quito...
...the Inca army numbered more than 250.000 experienced soldiers. Tupac ordered them to march against the men of Quito and the Cañaris. They encountered each other, both sides fighting with resolution and skill. The victory was for a long time doubtful because the Quitos and Cañaris pressed stubbornly against their enemies. When the Inca saw this he got out of the litter in which he travelled, animated his pepole, and made signs for the 50.000 men who were kept in reserve for the last necessity. When these fresh troops appeared the Quitos and Cañaris were defeated and fled, the pursuit being continued with much bloodshed and cruelty, the victors shouting “Ccapac Inca Yupanqui! Cuzco! Cuzco!”...
Thence Inca Tupac marched to the place where now stands the city of San Francisco de Quito, where they halted to cure the wounded and give much needed rest to the others. So this great province remained subject, and Tupac sent a report of his proceedings to his father. Pachacuti rejoiced at the success of his son, and celebrated many festivals and sacrifices on receiving the tidings.

After Tupac Inca had rested at Cuzco, re-organized his army, and cured the wounded he went to Tumipampa, where his wife and sister bore him a son, to whom he gave the name of Titu Cusi Hualpa, afterwards known as Huayna Ccapac. After the Inca Tupac had rejoiced and celebrated the birthday festivals, although the four years were passed that his father had given him to complete the conquests..."

Well, and after many other conquests...

tells the history that...

and to pleasing some authors...

tells the legend that...

"Tupac Inca Yupanqui is also credited with leading a roughly 10-month-long voyage of exploration into the Pacific around 1480, reportedly visiting islands he called Nina chumpi ("Fire Island") and Hahua chumpi (or Avachumpi, "Outer Island"). The voyage is mentioned in the History of the Incas by Pedro Sarmiento de Gamboa in 1572. Pedro Sarmiento described the expedition as follows:

…there arrived at Tumbez some merchants who had come by sea from the west, navigating in balsas with sails. They gave information of the land whence they came, which consisted of some islands called Avachumbi and Ninachumbi, where there were many people and much gold. Tupac Inca was a man of lofty and ambitious ideas, and was not satisfied with the regions he had already conquered. So he determined to challenge a happy fortune, and see if it would favour him by sea. … The Inca, having this certainty, determined to go there. He caused an immense number of balsas to be constructed, in which he embarked more than 20,000 chosen men; taking with him as captains Huaman Achachi, Cunti Yupanqui, Quihual Tupac (all Hanan-cuzcos), Yancan Mayta, Quisu Mayta, Cachimapaca Macus Yupanqui, Llimpita Usca Mayta (Hurin-cuzcos); his brother Tilca Yupanqui being general of the whole fleet. Apu Yupanqui was left in command of the army which remained on land.

Tupac Inca navigated and sailed on until he discovered the islands of Avachumbi and Ninachumbi, and returned, bringing back with him black people, gold, a chair of brass, and a skin and jaw bone of a horse. These trophies were preserved in the fortress of Cuzco until the Spaniards came. The duration of this expedition undertaken by Tupac Inca was nine months, others say a year, and, as he was so long absent, every one believed he was dead."

Many historians are skeptical that the voyage ever took place.

"Tupac Inca Yupanqui entered Cuzco with the greatest, the richest, and the most solemn triumph with which any Inca had ever reached the House of the Sun, bringing with him people of many different races, strange animals, inunmerable quantities of riches.
After Tupac Inca disembarked from the discovery of the islands, he proceeded to Tumipampa, to visit his wife and son and to hurry preparations for the return to Cuzco to see his father, who was reported to be ill. On the way back he sent troops along the coast to Truxillo(Trujillo), then called Chimu, where they found immense wealth of gold and silver worked into wands, and into beams of the house of Chimu Ccapac, with all which they joined the main army at Caxamarca (Cajamarca). Thence Tupac Inca took the route to Cuzco, where he arrived after an absence of six years since he set out on this campaign."

* This story of the navigation of Tupac Inca to the islands of Ninachumpi and Avachumpi or Hahua chumpi is told by Balboa (Cabello de Valboa) as well as by Sarmiento. They were no doubt two of the Galápagos Islands. Nina chumpi means fire island, and Hahua chumpi outer island.

History of the Incas - Pedro Sarmiento de Gamboa
Chapter 46, with a description of the islands of Avachumbi and Ninachumbi. Bracketed sentence in italics is as directed by the translator/editor, Sir Clements Markham, to indicate an interpolation into the manuscript by Sarmiento.

(1) In 1908 Dr. R. Pietschmann, Director of the Göttingen University Library, discovered a unique manuscript at the Royal Library of Copenhagen. Dr. Pietschmann in 1908 and 1912 called the attention of Americanists to this work, which was composed by a Peruvian Indian, Don Felipe Huaman Poma de Ayala ,and entitled "El primero i nueva coronica i buen gobierno". The manuscript is still in the possession of the Copenhagen Library where it is preserved with all the appreciation it deserves.