Why Endeavor Energy's founder sold his company after years of rebuffing offers

Autry Stephens agreed to sell Endeavor Energy for $26 billion in cash and stock to Diamondback Energy .

The 85-year-old wildcatter's decision to sell came after he was diagnosed with cancer, according to three people who discussed his health with him.

Interviews with 15 oil and gas executives, investment bankers and friends of Stephens paint a picture of an entrepreneur whose relentless work ethic and frugality have changed little since he became one of the richest people in Texas .