Dier is now in line for fresh contract talks at Tottenham, with Mourinho a keen admirer of his talents.
And Dier seems equally as taken with his new boss.
“He's a huge character, one of the most successful managers ever. It's a great pleasure to be playing under him," the 26-year-old said.
"When I look back I'll remember how lucky I was to play to play first under Pochettino and then Mourinho. It's a very privileged position to work under those two managers.
"Mourinho is someone, for me personally, who knows how to light the fire inside you. I want to win for him. I want to do everything to succeed to try and win with him and he builds that within you."
He added: “He's extremely motivated, extremely passionate about the game, about winning. His energy is very high everyday around the training ground, on the training pitch he's always pushing. I'm really enjoying working under him."