Marvel is the male tribute from District 1 for the 74th Hunger Games. Being from District 1 he is part of the Career pack and travels around with them.
Marvel is killed by Katniss Everdeen herself. Marvel catches Rue in a net and spears her, just as Katniss shows up. Katniss shoots Marvel in her anger, and he is the first person she directly killed.
Later when talking to Cashmere and Gloss during training for the 3rd Quarter Quell, Katniss feels very guilty about having been personally responsible for killing both the District 1 tributes in her first Games.