Koulibaly was born on 20 June 1991, to Senegalese parents in Saint-Dié-des-Vosges, France. His father worked in a textile mill in Senegal for seven days a week and never took weekends off for five years before he saved enough money to bring his mother to France. He grew up in Saint-Dié-des-Vosges, France, revealing that: “When you grow up in this environment, you see everyone as your brother. We are black, white, Arab, African, Muslim, Christian, yes — but we are all French. We are all hungry, so let’s go have a Turkish meal together. Or tonight, let’s all go to my house and eat Senegalese food. Yes, we have differences, but we are all equal.” Koulibaly says his upbringing was “heavily influenced by the multi-cultural nature” growing up. Koulibaly revealed that he first started playing football, saying: “All the kids were running around playing football with no shoes, and I was really upset by this, I guess. My mom says that I was begging her to go to the store and buy shoes for everybody, so I could play football with them. But my mother said, “Kalidou, just take your shoes off. Go play like they do.” In the end, I threw off my shoes and went to play barefoot with my cousins — and this is where my football story begins. When we got back to France, I was playing every day in the little park by our house.” His footballing career began with local club SR Saint-Dié. He then joined FC Metz in his first spell but when was released at fifteen, which according to the club’s Academy Manager, Denis Schaeffer, Koulibaly was let go “because he was too introverted, and his level was a little below our expectations.” In May 2019, it was announced that Koulibaly was named as an honorary citizen of Naples. In April 2015, he was previously named as an honorary citizen of Saint-Dié-des-Vosges. He is so popular in Naples that an entrepreneur created a pizza after him and Koulibaly himself has spoken of his fondness for the city. Koulibaly and his wife, Charline Oudenot, have a son together named Seni on 16 January 2016. He became a second time father when his daughter Nessa was born on 28 August 2019. He is a Muslim and states that his name derived from the Quran. In addition to speaking French, Koulibaly also speaks English and Italian. Throughout his time at Napoli, Koulibaly spoke out about racism in Italian football. In October 2019, Koulibaly called on the Italian football authorities to tackle racism by giving offenders a lifetime ban from entering the stadium. He had previously criticised the Italian football authorities for their lack of effort to tackle racism in January of that year.