Antonio Nieves is a ghost who appears in "El Muerto".
Antonio was an assistant coroner working under Grace Munoz. When he died he became a ghost, and remains in the morgue to help other ghosts to find closure and to move on. When Grace's own daughter, Laura, was hit by a car and died, he came to comfort her spirit each time she returned to the morgue. On the last such instance, he speaks to her about the Day of the Dead and of speaking to ghosts to help them find closure. She tries to follow his advice with a dead boy, but ends up frightened by him and blames Antonio for giving her bad advice.
Later, after successfully helping the dead boy to find closure with his father, Laura returns and he explains that the boy thought he was abandoned by his father, not realizing that he had died. Laura then realizes that Antonio himself is a ghost, which he confirms, and tells her that she, too, is a ghost. He prompts her, asking why she's so upset, and she reveals that she wished death on her mother just before she died, and she regrets it. Laura then communicates her love to her mother, and Antonio takes Laura away.