Eko, also known as Mr. Eko (also referred to as Father Tunde, although this may be an alias), was a notorious war lord and drug smuggler in Nigeria and was one of the tail section survivors of Oceanic Flight 815.
Before the crash, Eko was attempting to smuggle drugs out of Nigeria by pretending to be a priest. His brother Yemi, a real priest, tried to stop him, but was accidentally killed and thrown onto the drug smuggling plane. Eko was left behind, where he decided to take his brother’s place in the church, protecting it and the village from drug lords.
After the crash, Eko and the rest of the tail section survivors were attacked by the Others, where he fought his kidnappers and killed two of them. After this he took a vow of silence for 40 days and started carrying a stick with him into which he carved Bible verses. When Michael, Jin, and Sawyer washed up on shore, Eko kept them prisoner until they decided their story was true, after which they all trekked across the Island to the middle section survivors camp. He later found the Beechcraft his brother’s body had been on and burned the plane in respect. After he and Locke found the Pearl station, Eko was convinced it was important to push the button in the Swan. When Locke lost his faith and kept Eko from pushing the button, it caused the implosion of the Swan. Eko survived the incident, but was dragged unconscious into a cave by a polar bear and was later saved by Locke. While recovering from his injuries, he was visited by a vision of Yemi, who told him to confess his sins. Eko claimed he had not sinned, but done what he had to do, after which he was confronted and killed by the Monster. Three years later, Hurley saw a vision of Eko and played chess with him at the Santa Rosa Mental Institute.