39 years ago - Rex Mason is born.
16 years ago- 23-year-old Rex leaves the marines & becomes an adventurer.
14 years ago - 25-year-old Rex is hired to retrieve a hidden artifact by the father of his fiance Saphire Stagg. he is betrayed and exposed to the artifact's radiation, mutating him into Metamorpho.
8 years ago - 31-year-old Rex's longtime love Saphire leaves him. He leaves the Doom Patrol & is recruited into the Outsiders by Batman.
3 years ago - 36-year-old Rex saves most of the Justice League during the White Martian attack. Once recovered, he joins the new Outsiders where he meets Indigo.
now - 39-year-old Rex refuses to allow the Outsiders to destroy Indigo when her programming revolts against her, allowing her to rewrite her own programming.
Metamorpho was created by Bob Haney, who had previously found success with team books like the Metal Men and the Doom Patrol. Rex was designed to capitalize on that style of character. Obviously, he succeeded. While the character isn't a breakaway mainstream success, he's had prominent roles throughout his career, most notably as one of the Outsiders and an extended run in the Justice League. There's something inherently comicy about his design; the same sort of Saturday morning weirdness that permeates much of Haney's work, but re-purposed as a standalone character and turned loose to roam the DC universe. He's a fun mix of pathos and humor. It's very difficult to get him wrong.
There wasn't much we removed from his story. We did ADD a bit, by starting his early career alongside the Doom Patrol. He was deliberately designed to mimic their style so he's clearly a good fit for the team, especially in the years following the supposed death of the main team. Including Rex in that era gives the replacement lineup a certain tone that helps keep it feeling like the Patrol we all love.
The biggest change we've made is to have Sapphire leave him, which was done specifically to set up his relationship with Indigo. In Judd Winnick's Outsiders it was a duplicate of Metamorpho called Shift that fell in love with the android ingenue, a story that we absolutely loved. Rather than force that particular story into place we simply made Rex single so he could be in that relationship. We also gave that story a happy ending, because the relationship between these two characters is just the best.