The Argentine delivered Atletico's first La Liga in 18 years in 2014 - he was a combative midfielder in that 1996 title-winning team - and broke the Real Madrid-Barcelona dominance to win it again in 2021.
Yet after more than 14 years in charge, questions over Simeone's future are simmering, heightened by the arrival of new majority stakeholders at Atletico who may push for change.
The 55-year-old remains under contract until June 2027, but uncertainty surrounds what comes next.
Atletico sit fourth in La Liga and are 16 points behind leaders Barcelona, who they face three times in the next two weeks in La Liga and in the Champions League quarter-finals.
Against that backdrop, opinion among supporters is divided over whether the club's future should still be built around 'El Cholo'.
Atletico's transformation under Simeone
One thing that is indisputable is Simeone's managerial record at Atletico.
He has taken charge of Atletico Madrid on 786 occasions, recording 465 wins, 170 draws and 151 defeats across more than 14 and a half seasons at the helm. It makes him one of the longest-serving managers in world football.
Atletico offered Simeone his first big managerial job in European football when he was appointed in December 2011, his previous role on the continent having been to save Italian side Catania from Serie A relegation, following success in Argentina with River Plate and Estudiantes.
In that time, the club has been transformed. When Simeone first arrived, Atletico had just been eliminated from the Copa del Rey by third-tier Albacete and were 10th in La Liga, 21 points adrift of the leaders.
Yet under the Argentine coach, Atletico went on to win the Europa League in Simeone's first season, before adding the Uefa Super Cup and the Copa del Rey in 2012–13.
From 2013-14 onwards, after winning their first title under Simeone, Atletico have qualified for the Champions League every season, twice falling to agonising final defeats at the hands of rivals Real in the space of three years between 2014 and 2016.
Competing on Europe's biggest stage was no longer an achievement, it was considered the standard.
As Atletico supporter Guillermo Myela describes, Simeone changed the mentality of fans.
"We went from being 'El Pupas - the jinxed ones', to a club that can compete against Barcelona and Real Madrid without fear," Myela says.
"The connection that he has with the club and the fans is something that you rarely see in modern football. He lives for Atletico Madrid."
He is the most decorated manager of all time at the club and supporter Javier del Amo describes him as "one of the biggest icons in our history".
"One of his biggest achievements is getting the fans identified again with the team," del Amo says.
Lifelong supporter Dani Ruiz agrees: "He is the epitome of Atletico and what modern football has become."
New ownership, new opportunities?
For much of his 14-year tenure, Simeone's position at Atletico felt untouchable.
But cracks began to appear around 2022–23, as back-to-back seasons without major silverware and early European exits sparked doubts over whether the club's famed defensive approach had grown predictable.
He addressed the media at the time saying: "Since arriving at the club, I have given everything. I will always give everything, until the last day I am here."
Simeone is loyal to Atletico but hasn't hidden his desire to one day manage another of his former clubs.
"It doesn't depend on just me, but in my coaching career I can imagine myself managing Inter [Milan] one day. I think it will happen one day," he said in November 2025 before Atletico's Champions League tie against the Milan giants.
Those questions intensified again when, in March, new majority owners Apollo Sports Capital took control of Atletico, bringing fresh voices and higher expectations to the club.
Chief executive officer Miguel Angel Gil emphasised the need for consistency. He said he wanted "to continue to build on our great legacy on and off the pitch for our fans, our players, coaches and staff, and our community".
Yet this period of change has reignited debate among fans, who remain divided over whether Simeone should stay or step aside.
Fans thoughts - 'a toxic relationship'?
Fans like Ruiz think it should be up to Simeone to decide when he wants to leave: "He's been there to defend the fans and to embody what fans thought at the time. He means a lot to us and the fans love him.
"Those fans who have said he should leave over the past few years are a bit short-sighted. Simeone deserves to stay as long as he wants and he deserves to decide when he wants to leave himself. I would love him to stay beyond 2027."
Del Almo also agrees that Simeone will stay.
"I want what Simeone wants. He is so special for us so I want the best for him," he said.
"What is the best? Diego is the only person who knows that. Maybe his tenure is coming to an end at some point but Simeone and Atleti still have beautiful moments to experience together."
But Myela describes his feelings towards Simeone as being like a "toxic relationship".
"I love him and I cherish those beautiful memories that he created and will always appreciate everything that he has done for us. But I sometimes feel that the best for both would be to move on," Myela explained.
"The Simeone of 2026 is not the same guy who came to the club 16 years ago. A lot of coaches from other teams have already 'cracked his code' when it comes to football tactics, and his approach is not as innovative or efficient as it used to be.
"I have hope in the new management and I have faith that they are willing to invest in the club and make big signings. But I think that we need to adapt to current football and change our ways a bit."
For now, all of Simeone's attention will be on a demanding April for Atletico Madrid.
The Rojiblancos face Barcelona in La Liga this weekend, before meeting the same opponents in the Champions League quarter-finals.
Just three days after the second leg in the Champions League, Atletico will play the Copa del Rey final against Real Sociedad in Seville where Simeone will be aiming to add a ninth trophy to his Atletico managerial cabinet - decisions about the future can wait.
