Michael Crawford
Michael Crawford played the original Phantom in the first productions in 1986. He stumbled upon it mostly by accident, happening to run into Webber. Webber, who was familiar with Crawford's work in Flowers for Algernon told him he was writing an opera based off of Gaston Leoux's novel and wanted to know if he was interested. He told him was, and he landed the job as Phantom. He played as Erik for 2 and a half years, finally announcing his departure form the role by altering one of the lines in his last performance to, "Christine, I loved you." He was called back as a guest at the 25th Anniversary where he sang with the new stars in the Phantom world.
Ramin Karimloo
Originally, Karimloo played Raoul in Phantom of the Opera in 2003. He played the Phantom in 2009, his last regular performance as the Phantom. He became the first person to play the Phantom in the hit sequel to Phantom of the Opera, Love Never Dies. He played in that until 2011. What is believed to be his last performance in Phantom was on October 1 and 2, 2011 when he played the Phantom in the 25th Anniversary on Royal Albert Hall. He stated that it would be his last performance as the Phantom, but in a later interview he said, "Never say never." as a neither positive nor negative response to the question if he would be returning behind the mask.
Gerard Butler
Gerard Butler played the Phantom in the 2004 movie version. Before the movie, he'd had no other singing experience, but when Joel Schumacher (director of the 2004 movie) asked him about the role, he said he was interested and began taking voice lessons immediately. When he auditioned, Webber and Schumacher were impressed, and he landed the spot as Erik. He's now reportedly taking advice from Marilyn Manson, Jack Black, and Johnny Depp on how to become a rock star.
Hugh Panaro
Hugh Panaro played Raoul (1991) and Erik (1999) before leaving to claim the title role in Martin Guerre. He returned behind the mask in 2003 through 2005, when he left again to help create the Elton John Musical, Lestat. After doing multiple other Broadway shows in between, Panaro returned as Phantom in 2010 and even performed in the 10,000th production of the Phantom of the Opera in Broadway. He performed in the Broadway 25th Anniversary of Phantom. He's still performing on Broadway today.