The man who eventually became an infamous Islamic State executioner was once a high performing IT salesman, a former employer said.

The head of an IT company in Kuwait told The Guardian that Mohammed Emwazi was one of their top-selling sales agents before he went back to London in 2010 and did not return.

Emwazi was identified last week as the man who was previously known as Jihadi John, the militant fighter with the British accent who appeared in nearly all of the Islamic State's execution videos. 

Jihadi John is considered the foremost personality of Islamic State propaganda videos. He was first seen in the video depicting the execution of American journalist James Foley last year. He subsequently featured in various other Islamic State execution videos, the latest of which was the execution of Japanese journalist Kenji Goto on January 31.

His nickname was given to him by his former hostages, who said that Emwazi was part of a cell within the ISIS that was called "The Beatles." His nickname is a reference to John Lennon, one of the songwriters of the legendary British band The Beatles. 

"He was the best employee we ever had," Emwazi's former boss, who spoke on condition of anonymity, said of Emwazi. "He was very good with people. Calm and decent."

The IT company executive also described Emwazi as quiet and withdrawn, although he had surprising skills when it came to selling the company's IT products. However, he told the Guardian that Emwazi appeared to have a problem that he thought could be "family, social or psychological" in nature.

"I didn't really ask. He wanted a good job (in London) and he wanted to get married, but he couldn't and it made a problem for him," the executive told The Guardian.

Another former boss said that it was a puzzle for his company's staff that Emwazi came to Kuwait from London in order to find a job, as most Muslims or Arabs would travel the other way to find employment.