The drug smugglers were a group of three men - Eko, Goldie, and Olu - attempting to smuggle heroin, hidden inside Virgin Mary statues, out of Nigeria. The smugglers disguised themselves as priests and obtained control of a plane in their attempt to transport the heroin elsewhere.
After failing to smash open the glass window of the hatch with a trebuchet, Locke had a dream that night in which he saw the airplane crash landing on the Island. ("Deus Ex Machina") The next day, he convinced Boone to take a break in their efforts to open the hatch and search for the downed plane. As they closed in on its location, Locke noticed a rosary hanging from a tree branch. He gave a yank to a nearby vine and, to the surprise of Boone, a decomposed body - Goldie - in priest's clothing fell from the tree. In searching the body, Locke discovered a large wad of Nigerian currency as well as a handgun, making it clear the man was no priest.
Boone and Locke arrived at the plane shortly afterwards, discovering it suspended at the top of the tree canopy. At that point, Locke was barely able to walk, so Boone agreed to climb a tree and explore the plane. Inside, Boone found another decomposing body in priest's clothing as well as Virgin Mary statues lined with bags of heroin.
The smugglers acquired a quantity of heroin that for a variety of reasons, including lack of demand, needed to be moved out of Nigeria in order to be sold. ("The 23rd Psalm") At the time, U.N. and Catholic missionary planes were the only private planes allowed in the air. To complete their deception, the leader of the group (Eko) coerced his brother (Yemi), an actual priest, into providing them with the paperwork necessary to make them priests so they could board one of the planes allowed to leave the country.
Yemi arrived at the runway while the smugglers were loading the statues onto the plane. As he attempted to convince Eko not to get onto the plane, a truck filled with Nigerian soldiers drove onto the runway. Goldie and Olu exchanged fire with the soldiers, resulting in the death of at least one of the soldiers and the fatal wounding of Olu and Yemi. Goldie boarded the plane and helped Eko get Yemi onto the plane but kicked Eko out before he was able to board.
Eko later burned the plane with his brother inside.