"He certainly is different today from the way that I met him," Domscheit-Berg told ABC News. "It's either his way or the highway, so he can command everyone like in the military. We are not people like that."
Ironically, his former colleague says Assange became enraged over leaks about him he thought were coming from inside WikiLeaks.
"Was this you?" Assange wrote during an on-line chat with Domscheit-Berg just before their split. "I didn't speak to Newsweek or other media," he responded.
"I am investigating a serious security breach," Assange replied. "Are you refusing to answer?"
"He's not the best person to deal with criticism, I would say," said Domscheit-Berg.
The exchange ended with Domscheit-Berg writing, "You behave like some kind of emperor or slave trader." Assange answered, "You are suspended for one month immediately."
Assange Will 'Love A Show Trial'
Others who have split with him say Assange's ego is out of control.
"His specific words were, 'I am the heart and soul of this organization,' " recalled Herbert Snorrason, an Icelandic University student who was part of the group's security team. " 'If you have a problem with me, you can piss off.' "
The most serious issue, say former Assange associates, is the secrecy surrounding the group's money, where it comes from and where it goes.
"I'd like to know myself what has been happening behind the curtains," said Domscheit-Berg. Another of WikiLeaks' early leaders said Assange's goal from the beginning was to make a lot of money and seek personal fame.