R

R was an unidentified, possibly Dark wizard or witch who wrote letters directed to Jacob's sibling and Patricia Rakepick at the time they were at Hogwarts.

Biogaphy
This individual began writing suspicious letters signed as "R" to denizens of the Hogwarts School of Witchcraft and Wizardry in the mid-1980s. Those letters were very commanding, with imposed instructions and threatens of punishment in case the receivers did not follow the instructions. They first wrote to Jacob's sibling in the 1986–1987 school year. The following school year, they wrote to both Jacob's sibling and Patricia Rakepick, telling Rakepick to step away from Hogwarts.

Possible identities
The following individuals have been suspected to be R at some point:
 * Patricia Rakepick
 * Rita Skeeter
 * Merula Snyde
 * Albus Dumbledore