The electron mass in vacuum m _e is a fundamental physical constant. When electrons are moving in few-layer graphene sheets, their behavior gets strongly modified by the two-dimensional carbon lattice. Here I will discuss the capability to control the effective electron mass in few-layer graphene, and the unique physical phenomena emerging from such mass control: Electrons in monolayer graphene are described by a zero effective mass. Such massless Dirac fermions exhibit a linear energy dispersion and quantum critical electrodynamics. Bilayer graphene has a finite electron mass, and a widely tunable semiconductor bandgap can be induced through a vertical electrical field. Trilayer graphene, in contrast, features super-massive electrons at low energy. When integrated into a two-dimensional heterostructure with hexagonal boron nitride, the trilayer graphene can exhibit strongly correlated behavior and give rise to an electrically tunable Mott insulator.