The Green Skull is a bio-terrorist whom sees himself as a flowerchild of the 1960's. He briefly came into contact with Captain America when the later stopped a terrorist plot.
The Green Skull was created by Rick Remender and John Romita Jr. and first appeared in Captain America (volume 7) issue 1.
Major Story Arcs
Meeting the Captain
Green Skull first appeared on the scene while trying to kill the human population of New York so that nature could retake the island. He was stopped by Captain America and taken into custody.
Versus Sam Wilson, the new Captain America
Some months later, the Green Skull was seen again, apparently out of captivity, as he once more threatened the city of New York with his own made flying machine. This time, Sam Wilson, formerly the Falcon and now Captain America, took the Green Skull out and brought him into custody.