He is a large, mixed-breed dog who guards Brother Sam's body shop.
Eli was a witness when Brother Sam was shot in his garage after which Eli went to stand near Sam without barking at the shooter.
At the crime scene, Eli kept loudly barking loudly at the police, causing an annoyed Detective Mike Anderson to order the dog taken outside.
When Dexter attended the Candle Light Vigil for Sam, Eli barked at Dexter until Nick, a mechanic, quieted him.
Later, footage of Sam's shooting was found, and Dexter noticed that Eli was not barking. He knew that Eli barked at almost everyone except Nick and Sam. He realized that Nick was the shooter, and it was soon confirmed by both Sam (before he died) and Nick.