Koulibaliy also named Edouard Mendy and Jorginho as the Chelsea players who made it easier for him to join the west London club.
Chelsea officially announced the signing of Koulibaly on Saturday morning.
The Senegalese defender joined Chelsea from Serie A side, Napoli.
“It’s a big team in the world and my dream was always to play in the Premier League.
“Chelsea came first to get me in 2016 but we didn’t make it. Now when they came to me, I accepted it because they really wanted me to come to the Premier League to play for them. When I spoke to my good friends Edou and Jorginho, they made my choice easier, so I’m really happy to be with you today.
“I want to thank the fans because I saw a lot of them in London and on the plane everybody was happy for me to be here. So I want to thank them and I hope the season will be really good and we will give some good moments to the fans,” he said.