In the ancient Mayan empire, about a thousand years ago, he was a young, proud and very successful athlete. He loved his time in the sun, and never wanting it to end, he made a deal with the Mayan god Cacao, through the high priest for immortality (as well as enhanced physical attributes such as strength, durability, speed and stamina), in exchange for two sacrifices a year, one in the time of planting, one in the time of harvesting.
And thus he lived for centuries, traveling from culture to culture, being any form of sportsman he could find. And excelling in them all, he lived only for the game. However in the 1940's posing as a boxer called Kelly, he met Betsy and fell in love with her.
She did not learn the truth about him till she began to age and he didn't, however by this point the two were deeply in love. They ran about together, and every ten years or so he would emerge with another look and another name and be a different sort of athlete. However this put great strain on his marriage, as after she turned forty, Betsy had to pose as his mother. Eventually in 2013 after over a thousand years, he had changed, he was no longer just for the sports, he loved Betsy so much, and seeing that her time was coming to an end, he decided he didn't want to live on without her, thus he drove his car off a bridge, thus killing him and ending his long life.
However this was not the end; earlier on, thinking he would never die, he signed up to an organ donor's plan, thus with his death eight pieces of him were donated to other people, and the spell of Cacao passed on with the organs, granting each of them the same deal that Inyo had. It also dramatically changed them, and they all began killing to keep up with the sacrifices - they also gained a psychic link to each other and Brick's home, known as the "mothership".
Upon investigating, Sam and Dean learned from Betsy (now known as Eleanor Holmes) that the key was Inyo's own heart, if that died that all the others would die. Arriving at the location of the person who had gained the heart, Randa Moreno, they tried to kill her, however were ambushed by Paul Hayes and Jimmy Tagg (each had a transplant and had joined in the deal to become immortal).
With their enhanced physical attributes they managed to overpower the two, and with the other two holding Dean down, Randa tried to rip out Dean's heart. Sam recovered, and managed to distract Paul, freeing Dean's arm; Dean pulled out a knife and stabbed Randa in the heart, thus killing them all and ending Inyo's legacy.