Brig Gen Tlas, said to be in his mid-40s, is a member of Syria's most powerful Sunni family, which has given its support to the Assad's Alawite clan for decades.
The general's father, Mustafa Tlas, was Syria's longest serving defence minister, who helped to ensure Mr Assad's succession to the presidency in 2000 following the death of his father.
As a young man, Gen Tlas also attended military training with President Assad.
So, naturally, he was a member of Mr Assad's so-called inner circle, serving as commander of an elite Republican Guard unit.
The general - together with his wife - was also seen as a leading figure on the Damascus social scene, entertaining foreign envoys, artists and the media.
But sources say he has become increasingly frustrated in recent months over the violent crackdown by the security forces on protesters.
He was reportedly under a form of home arrest since May 2011, following his meeting with the opposition to try to start a political dialogue and also because of his opposition to the clampdown.
The current regime, he once reportedly said, was taking the country to hell.
Most of Syria's leaders are Alawite, but Gen Tlas is a Sunni Muslim, and his desertion may encourage other Sunni officers to consider their allegiances.
Manaf Tlas, a Syrian general, has deserted the regime of President Bashar al-Assad and left the country gripped by continuing unrest.