The New Cap (Mark Gruenwald Years Three and Four, Captain America 332-354)
In his third year on the book, Mark Gruenwald gave us a new Captain America. A Commission of Presidentially-appointed big shots (including the heads of the CIA and FBI) claimed government ownership of the Captain America name, costume and shield. They demanded that Steve Rogers once again work directly for the government, as he agreed to do when he was chosen to receive the super-soldier formula in World War II. However, Rogers no longer felt that Captain America should be a government propaganda figure, and resigned as Captain America. He was uncomfortable with taking his case to the people or fighting the government in court, and opted instead to assume a new, slightly different identity- the Captain:
Meanwhile, the government enlisted John Walker--the Super-Patriot-- to be the new Captain America (and his drinking buddy Lemar to be the new Bucky, later Battlestar). Walker took the job seriously, doing his best to live up to a legend he once mocked, and fought guys like the Watchdogs:
Unknown to almost everyone though, there were mysterious forces working to undermine Walker, and push him over the edge.
The nice thing about this storyline was that it meant Steve Rogers was absent from the book entirely at times, which was good because Gruenwald's depiction of Steve Rogers tended to be "dishwater dull" (in the words of one letter writer). The flawed (and sometimes brutal) John Walker was much more compelling. Of course, inevitably Steve Rogers reclaimed the Captain America identity (and not by brawling with Walker over the name, mercifully). And Walker is still floating around the Marvel universe in a modified version of Rogers' black outfit, under the name USAgent. He's had a couple of mini-series, and has been a member of the Avengers, Force Works, the Invaders, and Omega Flight. He's the Marvel universe's super-powered government hardass.