How Saladin became the ruler of Egypt part 1

General to Vizier to Sultan

https://www.youtube.com/watch?v=39yUoSEo6_0&t

How Saladin Became Ruler of Egypt Part 1 [Islamic History] - YouTube
Much is said about Saladin's Ayyubid State of Egypt and his victory at the Battle of Hattin. However, how did he become the ruler of Egypt in the first place......