Earl Ciel Phantomhive (シエル・ファントムハイヴ, Shieru Fantomuhaibu) born on December 14, 1875 is the business-savvy, egotistical 12-year-old (13-year-old as of chapter 14) and the head of the English Phantomhive noble family after the deaths of his parents, Lord Vincent Phantomhive and Lady Rachel Phantomhive. He runs the Funtomhive Company, which manufactures toys and sweets, with the later addition of a food branch after winning a Royal Warrant. His right eye, which is usually covered with a black eye patch, bears a pentacle, the sign of the Faustian contract he made with the demon Sebastian. Sebastian says that the mark on Ciel is proof of their contract. He also says that demons mark their prey so that they can locate them.

After his parents' deaths and prior to meeting Sebastian, he was a slave and a sacrifice in a cult ritual. During one particular instance where Ciel was being tortured, his hatred for his torturers summoned Sebastian. He then commanded the demon to kill all the people in the room. During his time as a slave, a mark was burned into his back; in the anime adaption, it is found on his left side, near his chest. In the manga the mark is found on the left side of his back. He does not want anyone to see this mark and appears to not enjoy physical contact (possibly aphephobic), though he tolerates Sebastian and does not complain when the demon picks him up or holds him. If stressed, he will slap someone touching him away, proclaiming "Don't touch me so easily!" He also once pointed a gun at Sebastian that he had hidden underneath his pillow, for he was having a nightmare of being tortured (supposedly provoked from reading Edgar Allan Poe before bed). This is a negative influence of the trauma he underwent during his time as a slave.

He is usually portrayed as emotionless, cold, boring, not fun, rude, and un-childlike, though he occasionally expresses concern for the well-being of the few close to him; Sebastian is not one of those people. He sometimes portrays himself as a happy person (mostly when undercover), but soon returns to his true self. Whether he worries for Sebastian's well-being or not is unknown, but ultimately he sees Sebastian as a pawn. Although, that said, there was one time that proved Sebastian was the most important person to him. There have been times when he wishes for Sebastian to fail at a task or request for humor's sake. He is close to his cousin and fiancée Elizabeth, seeing her as an annoying cute friend, the marriage was arranged. Before the loss of his parents, Ciel seemed to be a happy childlike child.