You've been linked with Chelsea for many years. Why did it finally happen this summer?
"It's true for a long time. The Premier League wanted me to come. But I believe in God, and I think the moment was now. Maybe before, nobody was ready, maybe Napoli didn't want me to come. I'm not a player who wants to go fighting with the club to leave. I have a lot of respect for the owner and the supporters, and I never fight with the club to go.
"I think this time was the good time to leave Napoli. I had eight years over there, and I had a lot of good moments with the supporters, teammates and staff. I learned a lot about football, but I think I was at the end of my story with Napoli. So I decided with my family and friends to come to Chelsea.
"Why Chelsea? I think it was because they were the only club that really wanted me to come. We had the first link back in 2015 when Antonio Conte came, they wanted me to come here. It didn't happen, but I was always linked to Chelsea, and this time was the right time. The stars were in a good line so I've come here and I am very happy to join Chelsea and the Premier League.
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"I want to thank everybody here at Chelsea because everybody was waiting for me to come. When I came, I was already home, so I am very happy to be here today."
At 31 years old, do you think Chelsea are getting you in your prime?
"I hope I will be here for a long time. It's true I am 31, but I know I can give some years here. I want to give everything for the club. They have a lot of confidence in me, so I want to show them on the pitch that they made a good choice. I will give my best to give everything because I am really happy here and I want to show everybody they made a good choice.
"This team is a fantastic team with fantastic players, winners. There's a big staff, big supporters, a big society, so I am really happy because from the first day I am like a baby in a shop. I am scoping everything, and I am really happy. I want to give them everything on the pitch, and at 31 years old, I am at a good moment, in a good city, and at a good club. So I want to stay a long time here."
How did the call with John Terry come about, and was that a nervous call to make?
"It's true I was nervous a bit because I was waiting to sign my contract with Chelsea. It happened the night before, at one o'clock. I was happy, and I wanted to know which numbers were free. The team manager told me some numbers, but he didn't tell me the 26, so I asked, and he said that John left it in 2017 and nobody had taken it from that time.
"I was asking whether it was retired or that nobody wanted to take it. I asked Gianfranco Zola, who I know well because we have the same person working on our business in Italy, I spoke to him and he told me the story of Chelsea because I need to know everything when I come somewhere. I asked a lot of questions to him about the club.
"I asked him for the number for John because I wanted to ask him about the jersey. He gave me the number directly, and I called him. In the beginning, he didn't believe it was me. He thought it was a joke, so he put down the phone and called the team manager to ask if it was really me.
"After I asked him respectfully that I wanted to take his number – and I know it was for him a very important number – but it is an important number for me because I took it directly when I went to Napoli, and I wanted to keep it here at Chelsea. When he told me yes, I was really happy because I know what he did for the club, the supporters, and the city here.
"It was very important for me to ask him and he gave me his answer. I was happy, and I wanted to tell everybody that I asked him before because I don't want to be disrespectful to a legend of the club."
You're replacing another club favourite in Antonio Rudiger, your clearly not afraid of a challenge?
"Antonio is a really good player. I like him, and I know what he did for Chelsea. I used to play against him when he was at Roma. He is a nice player, a good player, and did a lot here at Chelsea. I am happy for him that he joined Real Madrid, but for me, there is no pressure. I am happy to be here, and I do not want to be the guy who replaced Rudiger. I am Koulibaly.
"I don't have the same skills, and I don't play like him. If everybody wants me to play like him, I am not that person. I have another style. I will try to do my best to give solidity to the team. I know it will be difficult for me because I come from Italy, so I have to learn Premier League football, and it is very difficult.
"So it will be difficult, but I am really motivated, and I want to show that Chelsea made the right choice with me. So I want to show everybody I was ready to play in the Premier League and show the supporters of Chelsea that they can have confidence in me,"
You're going to be facing some of the best forwards in the world...
"It's good, I'm happy. I like duels and one-against-ones. I like to defend, so for me, it's the right place. We have a lot of good attackers here, and there are some of the best players in the world in this league. So it will be difficult for me, but I am easy. I want to show everybody that I can be the defender they think.
"I was excited to start because I want to play in the Premier League. I don't think too much about the other players. I think about my team, and I want to help my team and give something more to my team. This is the most important.
"I prefer to win every game even if we concede a goal, but my first idea is that we don't concede because if we don't, we have big players upfront, and they can score from everywhere. If we give this solidity at the back, upfront, they will have no worries in their head, and they will score a lot. This is the most important."
You've been hugely popular at your former clubs, and given the freedom of cities, do you think that can be the case here?
"I don't know, I will see. I discover everything in London. I am trying to visit the city, think about football, to feel the atmosphere of the city. It is different from Napol because, at Napoli, everybody was talking about football all the time. When I was taking my children to school, I was speaking about football with the other parents.
"I am discovering everything here. I want to take my time. I want to visit everything with my family and friends to feel the atmosphere."
How do you think you'll have to adapt your game in the Premier League and playing under Thomas Tuchel?
"I will have to adapt everything because the speed is faster. I have to think faster in my head, go faster, and move my eyes faster. This is more difficult for players in the Premier League. In Serie A, everything is more with the brain, calmer. You have to think of every movement.
"Here, you have to think very fast, and this is the first thing I have to change. On the pitch, the ball moves faster, and it's a new system for me, 3-5-2, so I have to adapt everything. I'm thankful to the staff because they gave me everything I need to understand. They talk a lot with me and the other players, Thiago and Azpi, they talk with me to help me adapt very fast.
"The most important is to have good behaviour to understand everything fast. I will need time for sure because I can't be the player everyone wants from the first game. I will take my time, and in two or three months, I will be the one everyone is waiting for.
"At the moment, I think game after game, and I'm thinking about Saturday. I am prepared to help the team if the coach gives me the opportunity to start. I will give everything for the team and the supporters."
It's a new era at Chelsea. What were the conversations like with the new owners, and what dream did they say they had for the club?
"They gave me a good impression. They are American, and when I spoke with the owner, he told me directly he wanted me. We didn't have a big discussion. He told me he wanted me to play for Chelsea and be part of this new era. It's true it is a transition, and everybody has to adapt.
"Maybe I am new in this club, but everything is new for everybody here because there is a new owner, and he is doing everything to make sure the team is competitive in every game. I think it will take time but the time will be good for everybody. It will be a good future for Chelsea and everybody."
Napoli owner Aurelio De Laurentiis said yesterday he wouldn't sign any African players if they wanted to play in the African Cup of Nations. What are your thoughts on that?
"It's up to him. For me, the most important thing is to respect everybody. I always respect everybody. When I played there, I was also playing for Senegal, and I won AFCON when I was playing at Napoli. It's true it was a difficult moment for them when we went to AFCON, but we won it, and I'm really happy today.
"We have to respect the national teams also. You cannot speak about an African national team like this, I think. You have to have respect as you have for the other national teams. As captain of Senegal, I think it's not a good way to speak about an African national team, but I respect what he thinks. If he thinks the team can play without African players, it's up to him.
"But I think not everyone in the club has the same idea as him. I know everybody over there, I know the supporters, and the supporters don't think like this. It's up to him, but it's not an idea of the society of the city, because the city is really respectful. This is what he thinks, not what the city is thinking or the society is thinking."
Did you have a conversation with Edouard Mendy before signing?
"Of course, Edou is a brother to me. We talk a lot about Chelsea when we were with the national team. When he was on vacation, he text me some messages, not pressure, but he was asking me to come and play with him at Chelsea. Jorginho did the same, so I had double pressure on me. But it was not bad. It was friendly.
"I like them, and they are very nice guys. I had good moments at Napoli with Jorginho. We spent many years together, won matches together, and spent many days together. When he asked me to come to Chelsea, I wasn't sure if the owner [De Laurentiis] wanted me to come or not. It started with Jorginho and then with Edou, all the time, he was speaking with me.
"As players of Senegal, we won AFCON together, and when I had the possibility to join him here at Chelsea, I was really happy. I remember in the last weeks, we were speaking a lot together to know if I was coming or not. When I signed, he was really happy because our family can spend more time together in London.
"And with Jorginho, I missed him a lot. When he left Napoli, I lost something. So I am really happy to be with these guys, and the team gave me a good welcome. So I am very happy to be here."
You are the fourth Senegalese player to play for Chelsea?
"It's true after Demba Ba, Papy Djilobodji, and Edou I am the fourth. It's good to be here because they had confidence in Senegal players. I also had pressure from my brother because he is a big fan of the Blues since we were children, and he used to watch the games, and he obligated me to watch the games.
"So I think it was destined, and when I signed here, he was very happy. I think this helped me a lot, and I think Senegalese people were happy that I signed for Chelsea. I made my choice more secure because I want to have love with me, so when I see Senegalie, people are happy for me to come to Chelsea, and when I got a message that Demba is happy, I signed here, I was very secure with my choice.
"I hope it can be more luck for the Senegal national team because I play with Edou here, so everybody will love Chelsea now. Also, in Napoli, the supporters said they would support Chelsea. So I am happy with my choice and that I will bring a lot of love with me. This was really important for me."
Were you ever asked not to play in the African Cup of Nations, and what did it mean to win it?
"No, never. Nobody ever told me not to go to AFCON. Maybe sometimes they tried to ask my agent, but with me as captain as Senegal, even as a player of Senegal, when AFCON comes, I want to be the first one there.
"In December, I was injured, so I came to Senegal early to start my training with the team. I was really happy and excited to start the AFCON. Nobody can tell me not to go to my national team. I have a lot of love for my national team, for my country, and for the people I play for. If somebody tells me not to go there, it's the only time I will fight with somebody.
"We are all respectful. We waited for everyone to come from the Premier League a bit late, but when everybody came, everybody was happy to be there. I think in Africa, we all think like this. We have respect for everybody, but if someone tells them not to come, they will all fight to come.
"It's the most important thing, and everybody has to give us respect like we give respect to everybody."
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