Undertaker (アンダーテイカーAndāteikā) is a nobleman and a funeral director who works with the underworld of Britain and frequently acts as an informant to Ciel Phantomhive. In the anime, he is also a retired, legendary Shinigami officer.
Undertaker seems to take joy in frightening others, as he seems to act creepy intentionally to provoke a reaction. He seems to enjoy both his job as a funeral director and as an informant to the Phantomhive family, as he has worked with them since before Vincent Phantomhive's time. He has great connections with the underworld, as victims of murder from the underworld often show up at his place of business. It is these connections that allow him to be a useful informant to the Phantomhives. However, he does not exchange his services for "the queen's money," as he seems to dislike of Queen Victoria. Instead, those who want information from him are expected to amuse him in some way.
He frequently refers to the deceased as his "guests." It is his hobby to remove organs from his "guests" for research. When living people come to visit him, he frequently asks if they came to see what it feels like to sleep in a coffin. He is shown snacking on bone-shaped biscuits and drinking tea from a beaker.
Undertaker has long grey hair with a few braids throughout, which is worn so as to hide his eyes. His eyes are apparently quite nice, as before Grell Sutcliff sees them, he calls Undertaker "dull," but after looking into them, he asks Undertaker to hug him(In the Funimation Dub/Sub the line is "Take Me"). He has a noticeable scar across his face, neck, and left pinky finger, although how he acquired them is unknown, and has long, black fingernails. He wears all black, including an incredibly long, black top hat, and he wears a long, grey scarf across his chest, with it knotted by his hips.
In the anime William acknowledged him openly as a former Shinigami but in the manga the mangaka has so far given only subtle clues such as drawing one of his eyes in the same style as the other shinigami (with a double iris, which none of the non-shinigami characters have) and showing that he can see the cinematic records of dead people. In the anime when he had not retired from being a Shinigami, he wore glasses and had silver hair even when he was younger.
In the manga, he was shown in the Phantomhive Manor along with other nobles and acquaintances of the Earl on Baron Kelvin's flashback, meaning that he was a possible acquaintace of Vincent Phantomhive.
In the anime, he is a retired, famous Shinigami, who was ranked management level and has judged souls as famous as Marie Antoinette and Robin Hood. William Spears says that even crying children would have offered their souls to him. He is highly respected by William, but he does not return the feelings, calling William "annoying and noisy."
As a Shinigami, he wore square, silver-framed glasses, and a black suit including a black trenchcoat. His death scythe looks similar to the stereotypical Grim Reaper's scythe, is silver, with a skull connecting the blade to the handle, which is wrapped in silver wires, like the bottom of the handle. As a Shinigami, he did not have the scars across his neck and face, but still had his ear piercings.
Presently, due to his status as a legendary Shinigami, he is still allowed in the Shinigami library, but he frequently forgets to return magic plays he borrows.