Eli was a character mentioned in dialog as being one of the passengers who sat in the tail section of Oceanic Flight 815. ("The Other 48 Days") Eli is considered an "unseen character" as no visible person was specifically associated with this name.
In their first night on the Island, three of the survivors were kidnapped by the Others. Two weeks after the crash, they struck again and nine more were kidnapped. Eli was among them, his name and description being on a list recovered from the pocket of a female Other who had been killed by Ana Lucia.
(At night on the beach, a roaring fire. Everybody sleeping. The camp is attacked and the kids and some adults are taken.)
Unknown Voice: Behind you! Behind you!
Emma: Help us, please!
Libby: The kids, they took the kids.
(Ana Lucia charges one of the attackers and hits her with a rock.)
Unknown Voice: They took Jim and Eli!
Libby: Nancy's gone. They're gone.
Ana Lucia: Which way did they go? Which way did they go?!!
(Grabbing the "other" she just hit with a rock)
Wake up! Wake up!! Who are you? Talk to me. Wake up!