The Portuguese tactician, who left Madrid to return to Chelsea this summer, was the one man who was given the most responsibility at the Santiago Bernabeu according to club legend Hierro.
"Every club is different and Madrid is even more so," he told Fifa.com.
"Madrid is a club where you have to win and it's a place that can wear you down - where people have a different way of thinking.
"If you were to ask me to look at the last 20 years in Madrid's history and say which coach has had the most decision-making power at the club, I'd say there's no doubt he [Mourinho] is the one.
"If you ask him though, perhaps he'd say he didn't have as much authority as he'd have liked. But everyone knows him perfectly."