#1 Christian Pulisic, Borussia Dortmund

Pulisic might not be the name one would want Liverpool to sign for sure in the summer but he fits several requirements at the Merseyside club both on and off the pitch. It is not often that a non-European player has 60 appearances for a top European club before turning 19. In fact, Pulisic is the first non-German player to do it in the Bundesliga.
The American joined the Black and Yellow in 2015 when Klopp was still the manager at Westfaldion. In a span of three years, Pulisic has become a key player for Dortmund, the main man for the US national team with seven goals and seven assists in their unsuccessful World Cup qualifying campaign and has the versatility to play in several attacking roles.
While Kylian Mbappe has stolen the headlines (for the right reasons, of course) in the past year or so, Pulisic could easily push him for being named as the best teenager in world football at the moment. A combination of pace, skill, vision and dribbling ability mingled with a strong work ethic and a humble personality define the 19-year old accurately as he continues to show maturity beyond his age.
Thus, he fits into Klopp's profile and the Reds boss can once again work with the talent he signed during his time in Germany. Further, Klopp's relation with Dortmund could act as a sweetener for the potential deal. Meanwhile, any asking price will be met with lesser resistance from the American owners, as they will see a lot of marketing potential in bringing their countryman to Anfield.
Hence, Christian Pulisic is a player Liverpool cannot afford to miss this summer and he has everything in his locker to become the catalyst for Liverpool winning the Premier League next season.