Stegron debuted in Marvel Team-Up #19 (1974), by creators Len Wein and Gil Kane. At the time, Marvel Team-Up usually starred Spider-Man in the lead role, paired with a different hero each month. This time out (to no great surprise) his guest star was Ka-Zar. Stegron could have easily gone on to become a Ka-Zar villain, but for some reason he's stuck mainly to the pages of Spider-Man's comics.
Vincent Stegron was an assistant to Dr. Curtis Connors (a recurring Spider-Man character best known as the Lizard). While working on one of Connors' tissue regeneration projects (those never go well) using dinosaur tissue brought from the Savage Land, Stegron had the idea to transplant dinosaur tissue into his own body. Well, it worked and he became the stegosaurus-type you see above. A man named Stegron? Transformed into a humanoid stegosaurus? How convenient.
At any rate, Stegron has a few interesting abilities, notably the power to issue telepathic commands to dinosaurs. He also has some fancy technology which can reanimate dead dinosaurs, even those reduced to skeletons (though it's a short-term effect). Stegron has effectively turned his back on his humanity and thrown his lot in with the dinosaurs, feeling they owe humans some payback for having been rendered virtually extinct.
Stegron appeared only about a dozen times in his first 30 years of existence, but he's been making the rounds in a few titles recently. In last year's Marvel Comics Presents#5-7 writer Christos N. Gage brought out a three-part Savage Land serial where various Savage Land denizens - Ka-Zar, Shanna, Devil Dinosaur, Stegron - joined forces to drive out Roxxon Oil (Marvel's all-purpose evil corporation). There was a memorable moment in the climax where Stegron animated an army of dead dinosaurs - essentially "zombie dinosaurs."
And where has Stegron been since then? Why, Christos N. Gage is far from finished with him! Check out this week's Avengers: The Initiative Featuring Reptil#1 to see Stegron as the main villain!