Captain America (vol. 1) #217 (Jan. 1978):
“The Search for Steve Rogers!”
by Roy Thomas, Don Glut, John Buscema, Pablo Marcos
15 characters in this story:
This issue introduces a SHIELD-sanctioned super-team known as the "SHIELD Super-Agents." The members of the team are Marvel Boy (Wendell Vaughn), Texas Twister, Blue Steak and Vamp. This was the first appearance of all of these characters, all of whom will go on to have long careers as Marvel super-heroes (or villains), although none would become so prominent as Vaughn (who became the super-hero Quasar).
As a group, however, the SHIELD Super-Agents will be a relatively short-lived team. The team will be disbanded after about a year (of publishing time), in Captain America #230, after it is discovered that the team was infiltrated by agents of the nefarious secret organization known only as "The Corporation."