The Big Man Majini is one of the types of Majini, infested by Type 2 Plagas.
As the name suggests, Big Man Majini are universally large males, who oddly show less signs of Plagas infestation than lesser Majini. They're all large, muscular men, who wear shorts but no shirts. In addition, Big Men never use weapons of any kind, but in the game Resident Evil 5: Gold Edition some of them do, preferring to get up close and personal and take down their enemies with their bare hands.
Although Plagas infestation is known to cause extreme resiliency and a slight increase in strength, Big Men demonstrate these traits far beyond those of their brethren. Big Men can take far more punishment than ordinary Majini, and a single punch is enough to send Chris Redfield, Sheva Alomar, Jill Valentine, or Josh Stone flying. They seem to count as minibosses in the same vein as the Chainsaw Majini (though much less resilient), as their corpses do not disintegrate after they are killed, and each Big Man drops a Jewel bangle treasure upon dying. However, the lone Big Man Majini on the port in Chapter 3-2 will drop a Gold ring upon dying.