#5 Ruud van Nistelrooy - 56 goals

Nistelrooy was the Champions League top scorer in the years 2001-02, 2002-03, 2004-05 for Manchester United. He scored 12 goals in the 2002-03 campaign for the Red Devils. Three consecutive years in the top scorer spot is more than enough to establish his qualities as a goalscorer.
Before Manchester United, he also appeared in the league with PSV Eindhoven, and after United, he went on to appear for Real Madrid. Finally finishing his career with an impressive tally of 56 goals.
#4 Karim Benzema - 56 goals

Benzema never gets the credit for his contribution to Real Madrid, but the striker has been instrumental in the club's success in the Champions League in recent times.
He is the fourth highest scorer in the tournament and has never scored less than four goals in a single season. In his initial days, he also appeared in the league as a player for Lyon.
#3 Raul - 71 goals

With a tally of 71 goals, Raul was the Champions League all-time top scorer for many years. He scored a hat-trick in his debut, and is also a three-time Champions League winner with Real Madrid.
He later also went on to appear in the tournament as a player for Schalke 04.
#2 Lionel Messi - 100 goals

Lionel Messi has scored exactly 100 goals in the Champions League since his debut in the 2004-05 season. He hasn't looked back yet and won the trophy four times in his career. He is the only player in the list to appear in the tournament with just one club - Barcelona.
#1 Cristiano Ronaldo - 120 goals

Ronaldo has been the top scorer in five of the last six season in the Champions League. In 2013-14 season, he made a record of 17 goal tally which makes him the most prolific marksman in the history of the UEFA Champions League.
His quality is evident from his consistency. He is a five time champion, his first one with Manchester United in 2008 and the next four with Real Madrid starting in 2014 and then three consecutive years in 2016, 2017 and 2018.
Conclusion
This year four of the players from this list will appear in the league once again giving them a chance to build upon their tally. Cristiano Ronaldo will appear for Juventus where he will face his former club Manchester United in the group stage. Messi, Benzema and Lewandowski will also appear for Barcelona, Real Madrid and Bayern Munich respectively.