The Phantom, known in life as Henry Ravenswood, was a human man who is now a ghost.
Having gotten rich alongside his brother Arthur in the Gold Rush of Thunder Mesa, arrogant and vicious businessman Henry Ravenswood took a wife in Martha and despite Henry's womanizing ways the two were blessed with a daughter, Melanie. Henry proved an obsessively protective father for Melanie, whom he saw as one more estate to be ruthlessly guarded. Over the course of her life, Melanie received numerous proposals, but all four grooms were murdered by the Phantom in secret.
Henry is believed to have died in the earthquake that sank part of Thunder Mesa into the bowels of the Earth, in 1860, though his ghost sometimes wearing a noose around his bony neck (à la Ghost Host) may hint at a somewhat different story. At any rate, following this death, Melanie thought she had found respite at last, but as she prepared to marry her beloved (Jake), Henry returned from the dead in the form of the skeletal “Phantom”, determined to continue ruling Thunder Mesa and his Manor with an iron fist even in death. The Phantom hanged Jake from the rafters of the Manor's attic (though one account[FANWORK] strangely states that he was possessed by the Thunderbird to do so, rather than acting of his own free will) and tormented Melanie all throughout the rest of her life, which she forcibly spent as a recluse, trapped in Ravenswood Manor by the Phantom and the various spirits he now commanded.
With complete, supernatural control over the ghosts of ruined Thunder Mesa and of Ravenswood Manor — now known as Phantom Manor — the Phantom continued to act as a sepulchral tyrant for Melanie, still refusing to let her escape the Manor. That the Manor came to be transported to Disneyland Paris made no difference to the Phantom, though he enjoys the opportunity to let "curious guests" take a tour of his home, so that he may terrify them.
Behind the scenes
The Phantom was created as the main antagonist of the Disneyland Paris ride Phantom Manor, which opened in 1992.
He is functionally the Phantom Manor counterpart to The Haunted Mansion’s Ghost Host, and returns to early concepts in the Mansion’s developments that would have revealed the Ghost Host as an explicitly sinister, murderous figure responsible for the ghostly Bride's doom.
Bringing things full circle, Henry Ravenswood was himself the inspiration for a new character in another attraction: Barnabas T. Bullion, introduced in 2013 to Big Thunder Mountain Railroad. Though both are Gold Rush-era businessman exploiting a mine in Big Thunder Mountain, and overprotective of their respective daughters, Bullion is a more sympathetic character by far, and in no way murderous or supernatural. Though one might think otherwise, the existence of Ravenswood and Bullion aren't contradictory to each other, as the Ravenswood Mine was exploited until 1860, whereas, per the comic, Bullion's mine had its heyday in the late 1870's, long after Ravenswood's death.
His backstory was kept ambiguous in the ride's original form, though the Imagineers' original intention that he was Melanie's father Henry was released in other media, such as the short story Family Secrets, and remained hinted at in the ride itself. The 2019 refurbishment of the ride (in honor its 30th anniversary) confirmed the link, much to the ire of some people (fans and Imagineers alike) who had grown fond of the idea that the Phantom was instead an unrelated spirit, with a Phantom of the Opera-esque romantic interest in Melanie. Indeed, several bits of merchandise and live performance in the Park (such as the film Let's Go to Disneyland Paris (1993) had hinted at such a relationship between Melanie and the Phantom, up until a few months before the reveal of the 2019 refurb's nature.