From Sonic Retro
Originally designed as a characterization of the rabbit animal that is freed from badniks in Sonic 1 and 2, he became a major character as the comic progressed. His first major appearance was in issue 8 where Sonic, Tails, himself and Porker Lewis travelled to the Special Zone. After Dr. Robotnik sent them into the future where he ruled, Johnny became one of the Freedom Fighters.
He donned a red leather jacket with Sonic's head stitched into the back, and a metal staff that he sometimes uses as a weapon. Although not a central character, he usually contributes to the fighting and helps Sonic out. One of his major achievements was thwarting Brutus when he had his mind taken over (to find out the location of the Emerald Hill Zone folk); Brutus was unintentionally affected by his kindness and he destroyed many of his own troopers. Eventually he had to destroy the device and in turn he lost the knowledge of the Emerald Hill Zone people (who where hiding on the Floating Island).
In another story involving him, a mysterious creature called Shady copied his likeness and went under the alias 'Agent X.' and captured Sonic. Sonic and the real Johnny eventually defeated Shady and returned from the Shadow World as normal.
Finally, during the Chaos Saga, the Freedom Fighters were battling Chaos, and Johnny heroically sacrificed his life to save the gang and (temporarily) defeat Chaos. This was a shock to the readers as one of the longest-running characters had died. The comic finished soon after, leaving a bitter taste in many readers' mouths.
Amusingly, Nigel Kitching (the writer of the Chaos Saga) killed off Johnny because he found him "Dull and boring, he never did anything useful." Despite his death, Johnny Lightfoot is still a fan favorite with many StC readers.