Unhelped by Chelsea's poor opening to the new season, the Senegalese captain has dipped in and out of form, demonstrating the top of his defensive ability and at times, his worst.
But when the 31-year-old does manage to reach his peak, he looks like one of the best in the world, and perhaps his biggest inspirations have a lot do with that.
"Marcel Desailly and Lilian Thuram," when asked on his heroes for the official Chelsea matchday programme (via the 5th Stand app). "I was French, I am French. I was born in France, so I grew up with them as my example, and it helped me a lot.
"As French guys with African origins, I was watching them like big stars, idols. Today, I speak with Lilian Thuram and he gives me a lot of advice, a lot of help."
Koulibaly was the only one out of the three to choose to represent his African roots and has been captaining his side since 2019.
On the decision to wear the colours of Senegal, he said: "It was a big, big choice because I could have played with the French national team, but at 23 or 24 years old I decided to play for Senegal because they were waiting for me.
"When I arrived [in Senegal] and I saw the other players, it was like they were my family, because we were all used to eating the same things at home, to speaking the same language at home, so for me it was like I was home.
"I said to myself, 'Why didn't I come before? They are like my brothers'."
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