He appears in the pages of Teen Titans in the New 52 after Bunker posted an ad on gregslist.com looking for potential teammates. They met at Radu's before Bunker brought him up to the penthouse where he revealed his true colors and attacked the other members of the team. He was defeated by Wonder Girl.
Eddie Walker was a homicide detective working for a division of the Metropolis Special Crimes Unit (trained to deal with anything from meta-human crime to alien invaders), led by Maggie Sawyer. Walker became known as the department's volatile "Loose Cannon" for his reckless attitude. Tragedy struck when Eddie was crippled in a car accident, and he was given a desk job. Suffering from deep depression, he considered suicide, but Eddie was luckily contacted by Maggie before he could bring himself to carry it out. Maggie asked Eddie to investigate a slew of murders in a homeless district. Unbeknownst to anyone, these murders were actually the work of alien parasites who'd come to Earth to drain the spinal fluids of humans. Eddie ended up being attacked by two of these parasites, but instead of dying, the crippled detective ended up inadvertantly gaining the ability to transform himself into a superhuman giant. With his new powers, Eddie teamed-up with the Eradicator (who was filling in for Superman at the time), together they were able to drive the aliens out of Metropolis. With a new lust for life, Eddie dubbed himself "Loose Cannon," and took part in ridding the world of these alien parasites for good.
During Infinite Crisis, Eddie was part of a small team of heroes (including Roy Harper) who were contacted by Oracle in order to prevent the Secret Society of Supervillains from causing a massive breakout at the superhuman prison known as the Slab. Eddie and his team were able to defeat some of the prisoners, but several still managed to escape. He also aided in the effort to clean up Bludhaven after it had been bombed.
Eddie was later seen attending a special mass that was held to honor the heroes who'd gone missing or perished during Infinite Crisis.
One Year Later, after Infinite Crisis, it was revealed that Eddie had fallen prey to organ thieves who'd harvested his super powered heart. He was later revealed to have survived this by being put on life support.
The New 52
Loose Cannon in his teenage persona infiltrated The Teen Titans. He attempted to kill Robin while possibly under the influence of N.O.W.H.E.R.E. Robin was able to subdue his assailant. Loose Cannon has not been seen since.
Powers and Abilities
Eddie Walker was originally able to turn into his Loose Cannon persona only at night, and would be forcibly turned back into his crippled human state once daybreak hit. As Loose Cannon, Eddie Walker has considerably increased size, strength, durability, stamina, and regenerative healing capabilities. Eddie changes color as when he gets angrier, and each colored state makes him progressively bigger and stronger. His colored states go from blue to purple, to red, and lastly white. His white state is his strongest and is only brought on by extreme rage; this state is unfortunately considerably dangerous, as Eddie can barely form a coherent thought while he's in it. Loose Cannon's strength level has yet to be gauged, but he has been shown to be strong enough to match the Eradicator.