Team Flash is getting a makeover. With Wally gone and Harry back on Earth-1, S.T.A.R. Labs was already going through some changes before Ralph Dibny was invited to join Team Flash in "Elongated Journey Into The Night." And yet, at the end of the episode Barry asks Ralph, aka Elongated Man from the comics, onto the Team as a trainee. So, just who is Elongated Man on The Flash? Well, firstly it's important to note that he technically hasn't gotten the name Elongated Man yet. (Barry suggested "Plastic Man," but that didn't sit right with Ralph.) But, it definitely looks like he's going to earn his superhero name sooner rather than later.
Ralph used to work as a Detective alongside Barry and Joe at CCPD, but got fired after he tampered with evidence in order to frame a man he believed was guilty of murder. As the son of a man in jail for a murder he didn't commit, a rookie Barry Allen wasn't willing to let this go. He turned Ralph in and lost him his job. This was all years ago, before fate brought them back together again. Ralph, it turns out, was one of the passengers on the bus that got hit with the dark matter when Barry ran out of the Speed Force, and he's a metahuman now. Unlike the previous new metas, Ralph doesn't realize he has any new abilities until he's dangling out a window, slowly watching his torso stretch him all the way to the ground. That's right: he's elastic. Every part of his body can stretch to untold lengths. The only problem is, he can't control it.
Barry and Joe get Ralph back to S.T.A.R. Labs for examination, and Caitlin is able to get his cells to stabilize, but Barry still doesn't trust Ralph. He's convinced that Ralph is going to use his powers for evil, and that they should just lock him up now that they have the chance. Caitlin, however, is adamantly opposed to the idea, which sends Barry and Iris looking for dirt on Ralph. What they find out: someone wants him dead, and it has something to do with the mayor of Central City. Barry is quick to judge Ralph for blackmailing the mayor (Ralph has been working as a Private Investigator and obtained photos of the mayor cheating on his wife), but in the end, Ralph decides he doesn't want to be the man he was before. Ralph calls off the blackmail, but the mayor still tries to kill him, and when the Flash shows up to help, the mayor kidnaps Joe to make a clean getaway. With Elongated Man's help, Barry is able to save Joe, and the experience inspires him to offer Ralph a spot on Team Flash. He wants to train Ralph to be a superhero like him.
Ralph accepts Barry's offer, giving Team Flash a new ally and a juicy piece of information. When Barry asks who hired Ralph to spy on the mayor in the first place, Ralph says he never met the guy. All he knows is his name: DeVoe. The name triggers a memory in Barry from his trip to the future last season, when he was attempting to stop Savitar. His future self mentioned making a "cerebral inhibitor" to take down DeVoe. Barry doesn't know it yet, but DeVoe is actually the Thinker. It's Barry's first clue about the new big bad.
Until now, all Team Flash knew about their current threat was that someone manipulated them into creating a busload of new metas. Now, thanks to Ralph, not only do they have a name — DeVoe — they also know that their new villain is purposely putting the new metas in their way. DeVoe didn't just turn Ralph into Elongated Man, he also manipulated him to spy on the mayor, thus inserting Ralph into Barry's life. It's unclear why DeVoe would want Barry to train Ralph. Maybe he thought Barry would throw him in jail with the other two new metas, or maybe this is all part of a much larger plan. One thing's for sure: whatever he's planning, it can't be good.