Who did Thomas Jefferson mold the separation of powers idea from when he wrote the Constitution

Probably the two main reasons that separation of powers changed from a popular theory to a vital principle of government were 1.) that the state leaders had within their reach, through election either by the houses or by the people, the office of governor, and 2.) it was generally accepted that the executive office was the place for leaders whether they were radical or conservative. Consequently, radical leaders such as Patrick Henry and Thomas Jefferson became governors and supporters of separation of powers in their efforts to strengthen the executive. On the other hand, the conservative Roger Sherman did not become governor and continued to oppose separation of powers. 8 Had the executive office been unattainable in America because a king occupied the executive position, or weak because a king controlled the incumbent, then the services of popular leaders would have been limited to the legislative branch. Under these circumstances the supremacy of the legislative branch would probably have been established.