The player takes the role of various heroes from the Medal of Honor series. There are three different campaigns, each with its own hero that spearheads squads to complete objectives. These heroes are: Lieutenant Jimmy Patterson, who was the star of the original Medal of Honor and Medal of Honor: Frontline, Sergeant John Baker from Medal of Honor: Allied Assault - Breakthrough, and Lt. William Holt from Medal of Honor: European Assault. The campaigns take place in Italy, Holland, and in Belgium.
Source: Wikipedia, Medal of Honor: Heroes, available under the CC-BY-SA License.