Pre-Crisis of Infinite Earth
Tracer was a terrorist on the planet Angor and belonged to a group called the Extremists. The group tried to take over the world but failed. Tracer and the other Extremists, except for Dreamslayer , died on the planet Angor after the group caused a nuclear holocaust.
Tracer was recreated as a robot along with the other dead Extremists by his former teammate Dreamslayer. Once the team was recreated and functioning they attempted to take over the Earth. They were ultimately stopped by Justice League Europe . Once defeated the Extremists robots were taken to Paris to reside in Madame Clouseau's Wax Museum for display. The team was later reactivated by Dreamslayer for a second time on the island of Kooey Kooey Kooey , and later reactivated again to be used by Twilight in a battle with Supergirl.
Post Crisis of Infinite Earth
On Earth-8 solider Vincent Cable tried to desert his post and was badly injured. Experimented on by his government Cable was mutated and forced towatch violent images and subliminal messages teaching him how to kill. They did their job too well as on his first mission Tracer turned on a teammate.
Before he could be shut down via the control chip the government had installed Lord Havok appeared and destoryed the chip offering Tracer a place in his organization as an Assassin. Tracer takes the job and works for various officals gathering information on them which he sends to Lord Havok.
In issue #3 of the Lord Havok and the Extremists Countdown tie in Tracer is beatern by Monarch and only survives due to his healing factor. He continues to server Lord Havok on Earth- 8 with his Masters plan to take over the multiverse.
Tracer started out in Justice League Europe issue 15 and was a member to the Extremist. He was kind of taken as a dark joke. In the first appearance the rest of the team threaten to torture him for killing the last human on Angor, a fate he escapes by sensing Silver Sorceress is near by. Then in the fight with the JLE, Tracer is beaten by Rocket Red and after they beat the JLE the Extremist argue over who will pick up Tracer's beaten body, showing they care little about his health.
Then in Post Crisis Tracer was made more tougher and more hardcore. He was was given a back story and more abilities. Many say he was DC's version of a Wolverine/Saber-tooth cross.
Superhuman strength, enhanced speed, blades on his hands, claws, healing factor, agility, super senses and animal instincts. He has a set of wrist blades.
Justice League Unlimited
Tracer appears in the Justice League Unlimited episode "The Cat and the Canary" as one of the metahumans contestants in Roulette's Metabrawl. He later reappeared with the rest of the Extremists in "Shadow of the Hawk", when they attacked a city and battled the Justice League. During the fight, Vixen conjured a boa constrictor and cut off his air supply. Tracer was presumably taken into custody after this.