One of the most memorable Gruenwald storylines was "Cap No More" (Issue 332 till 350) wherein the US Government discovers the secret identity of Captain America and subsequently declare the costume, shield, and very symbol that is Captain America as government property. In order to retain the persona of Captain America, Steve Rogers was ordered to serve as a government agent answering only to the Higher Commission, a group of suits in charge of super human activities.
With the United States being a free country, Rogers envoked his right to choose and after 24 hours gave up the uniform and shield of Captain America. After several weeks, Rogers emerged as "The Captain" (US Agent's costume for those of you who are unfamiliar with "The Captain") and armed with a Vibranium shield provided by Stark Enterprises, The Captain went after a number of villans like the Serpent Society, Famine of the Four Horsemen of Apocalypes, Crossbones, The Red Skull, etc. The Captain was not alone in his crusade as his comrades: The Falcon, Nomad, Vagabond, and "D-Man" Demolition Man weren't that far behind. This particular storyline concludes in issue 350 wherein the clone of Steve Rogers who was actually the Red Skull pitted Johnny Walker, The New Captain America against the old Captain America, Steve Rogers "The Captain."
Both Rogers and Walker were able to work together to defeat the Red Skull and the Commission, deemed Walker to be too volatile as Captain America and gave the role as well as all the rights and privilages back to Rogers who resumed his role as the original Captain America. Not long after, the Commission orchestrated a mock assassination on Walker and bought the rights to Roger's "The Captain" costume and subsequently gave it to Walker who underwent speech and movement therapy to change his voice as well as his mannerisms.
