The 25-year-old has put pen to paper on a long-term contract with Liverpool and will begin life at his new club when he concludes international duty with Colombia.
Diaz faced the Reds twice in the Champions League with Porto earlier this season and Klopp admits he is a player who has long been on the club’s radar.
“I could not be happier that we’ve been able to get this deal done and bring Luis to Liverpool,” the manager told Liverpoolfc.com.
“I have always been a believer in only signing players in January if you would want to sign them in the summer, and that’s very much the case with Luis.
“He is an outstanding player and someone we’ve been tracking for a very long time.
“We believe he has everything needed to fit into our way and adapt to the Premier League, both physically and mentally. He is a player who is hungry for success and knows you have to fight to get what you want. He is a fighter, no doubt. He’s a skilful team player who has always the goal in mind.
“This team deserved to add quality and when we played against Luis earlier this season, we saw what a danger he is, how fast he is and how his mentality was to help his team.
“We know Porto is an outstanding club who nurture players in the best possible way and provide a brilliant football education. They are a class club and, I have to say, have been tough negotiators.
“We also have to say thank you to the Colombia FA for being so helpful in allowing us the time to complete this deal. They have a big game on Tuesday and I know as well as anyone how important preparation is for matches, so for them to allow us a few hours to finalise the transfer without impacting their training was greatly appreciated.
“I also must make clear my appreciation to our ownership and football operations team for how they have managed to act so decisively to get this done.
“Luis is a player we believe will make us better now and in the future. He is the player we really wanted and they’ve made it happen, so I am very happy.”