Zinedine Zidane was one of the greatest players of All Time. He was 3-time Player of the Year. Won basically every trophy. Scored goals in World Cup Finals and Champions League Finals. He was signed by Real Madrid during the height of their Galactico era, and scored the club's biggest goal of hte 2000s, his scintillating volley (from his off-foot - though with Zizou, there was no real off foot) to give Madrid a 2-1 lead against Bayer Leverkusen. He did all of that, but his lasting legacy at the Club may actually end up more important as a manager.
Zinedine Zidane accomplished a lot in his now eight months managing the club, from steadying a sinking ship to the point they came whisker-close to catching Barcelona for the La Liga title, to navigating injuries and pressure to win the Champions League - the prize Real Madrid cares about more than any. He was hailed for his ability to manage that locker room full of stars who's interests have often seemed to veer away from what is best for the club. Of course, there were detractors, marking Madrid for taking advantage of an easy path to the Champions League title, or noticing Zidane did little in terms of his formations and team selections that actually changed.
But no matter his tactical abilities, which should only improve over time, he has definitely done the biggest thing that anyone at Madrid can do, and the one thing the Hall of Fame level managers that preceded him (specifically, Carlo Ancelotti and Jose Mourinho) were unable to do: He took on Florentino Perez's way of running the team, and seemingly won. Zidane is the one driving Real Madrid now, and even if the results don't match Perez's continually-too-high expectations, the process is right and the process can set Madrid back on course for the long term.
Now, this may not last. A run of a few bad weeks, or a trophy-less season, will likely still end with Florentino Perez sacking Zidane and going with another manager who will likely be more subservient to Perez's will. But until that happens, Zidane has really done more to claw away power from Perez than any previous manager. Zidane got his wish to stop Real Madrid's lavish, often unneeded spending in the offseason. The stunning lack of signings by Madrid was almost seen as Zidane pushing way too far the other way, but Zidane's response was simple "I believe I have the players I need. Anyone we sign would be extra and would not have a place." That is not to say Madrid did nothing. They signed Alvaro Morata back from Juventus for good, and signed back Ascensio as well, a young 20-year old ex-Madrid academy player. That's basically it.
He came into a picture of a team with way too many attacking players and way too many midfielders, and precious few players who would track back and work hard. Why is this? Because previous regimes that were controlled by Perez and his affinity to sign big names, traded away these types of players (Xabi Alonso, most notably) for the other (Toni Kroos). Of course, nothing was worse than James, a player who had a nice few years at a small club, an admittedly great 2014 World Cup Performance, and then just had to be signed by Perez. Since then, he gained weight, developed a "night-life" problem, and became something of a team pariah. In the biggest sign of Zidane's power, he took James and planted him on the bench from Day 1.
Zidane has proved to be incredibly deft with the notoriously sharp and awful Madrid media. He has consistently said that James fits into his plans, and James has a future in Madrid - while also saying James has to earn that future. And by Zidane openly not playing James, even when the team is injured and normal Starting spots are open, Zidane is not only sending a message to James, but sending it indirectly to everyone. Real Madrid is a meritocracy (apart from, probably Cristiano), and the best players and the ones that buy in will play. It is a warning shot to Benzema, that Morata is here to play and steal your time if you aren't dedicated. Think I'm bluffing, look at James over ther! James actually might be more valuable to Zidane as a sign of his power and a sign of his honesty than as an actual player.
More than just James, it is the reliance on Casemiro (and if Zidane could, that is the type of player he would sign to get depth in the defensive midfield), and Lucas Vazquez, Martin Kovecic and now Ascensio over players like James and Isco. Not that these are great players, but they are young, they are moldable, they play defense, and they are products of Madrid's academy. They are everything Zidane wants in a player, and everything Perez-era Madrid does not. And Zidane is winning by playing them.
Madrid has never really looked at the long game in recent years, but you can see Zidane almost plan right now for life after Cristiano, First is his close tie with Gareth Bale, a player he pushed hard to be signed when he was Sporting Director (a fairly meaningless, honorary title at Real Madrid), and created a close connection with when he took over. Then his collection of hard working wing players who could slot into Ronaldo's role - obviously offering a very different (and admittedly not as good) skillset, but positional fit nonetheless. Ronaldo can play by his own rules because he is one of the best of all time as well, but his days in Madrid may be numbered, and Zidane is setting this team up to be young, deep, variable and ready to take over even if Ronaldo were to exit.
Zidane obviously has qualities apart from his political skills (incredible valuable at Madrid) and tactical knowledge (which is still being proven) that make him a great manager, but none has been better than his temperament and ability to connect to his players. His temperament has been so calm, so steadying (in hilarious contrast to his playing days, where his short temper was his biggest failing). He never swayed from his mantra of the process favoring the results, from his team getting better each week, from his team always having to work. It was that mindset that nearly corralled Barca and won the Champions League despite having to overcome a 0-2 1st Leg hole in the Quarters. But the real key is that ability to connect.
In-game management by coaches is overrated. Even tactical brilliance is overrated - there is no clear sign one way of playing is any better than the other. What matters is knowing your players and knowing how to deploy them and motivate them. Zidane has been amazing at this. His players have adored him from Day 1. So often we see All Time Greats try coaching to little success, and a large reason has always seemed to be the distance between them and the peons they are coaching - whether it be Diego Maradona, or Wayne Gretzky. Zidane may be helped by the fact he coaches a team of superstars that knows what it is like to have that prodigious talent (Ronaldo clearly respects him to a level he may not have previous coaches in Madrid), but Zidane also has been able to connect to them as an ex-player.
It remains to be seen how this will all work. Madrid still has weakness in the back, and as much as he might have them try to cover them up by having his best players track back more, those are still issues. The team still is not deep in those areas, and injuries to his back line (or God help him if Casemiro goes down for a long period) can be the death of the team. But he has already shown an ability to adapt to changes in personnel.
A few years from now, if Zidane succeeds at Madrid it will be because he does have a certain style of play he favors, and maybe he is waiting to get his players to play that style. Yet even there, his ability to fit his current roster to a certain way of playing is a sign of a great manager. He didn't need to make whole-sale changes, he could be flexible enough to play with the resources he had. Zidane is putting in place a methodology, a sense of calm and security and direction, that Madrid has sorely lacked. If he can show himself as a tactician, or hire assistants to do this for him, he really would check every box as a manager. The future has never been brighter at Madrid, and all it took was for Madrid's first true Galactico to come back and end the Galactico modus operandi that Florentino Perez controlled for good.