Rubinstein worked as a hardware engineer at NeXT and later joined Apple once Steve Jobs returned to the company. Apple announced Rubinstein's retirement in 2005. By that time, he was Senior Vice President of Hardware Engineering. In 2007, Rubinstein decided to join Palm as executive chairman of its board of directors.
As Brent Schlender and Rick Tetzeli explain in their upcoming book, Becoming Steve Jobs, Rubinstein had emailed Jobs the year following his departure to let him know that he had been hired by Palm. It only took about four seconds for Jobs to call Rubinstein after he sent that email.
"He couldn't understand," Rubinstein told Schlender and Tetzeli. "He said, 'You've got plenty of money, why are you going to Palm?' I'm like, 'Steve, what are you talking about? I mean, you've got orders of magnitude more money than I have and you're asking me? Are you joking?"
To Jobs, the move was like treason and the two never spoke again.
The book, Becoming Steve Jobs, appears to have a host of interesting new tidbits about the Apple co-founder's life. You can pre-order it here.