|"We must've been through hundreds of books already and we can't find him anywhere —"|
Rosier is the surname of a pure-blood wizarding family, and one of the Sacred Twenty-Eight. They are related to the Black, Lestrange and Malfoy families. Given these relations, as well as the participation of two Rosiers in the First Wizarding War as Death Eaters, it is likely that the Rosiers place great importance on their pure-blood heritage, disdain Muggles and Muggle-borns, and practise the Dark Arts.
It is likely that members of the Rosier family have thick eyelids, as two of the daughters of Druella Rosier and Cygnus Black were described as having "heavily-lidded eyes" by Harry Potter. It is unlikely that this is a characteristic inherited from their father's side as no mention of this physical feature is ever made in relation to any member of the Black family.
- Druella Black née Rosier — wife of Cygnus Black III, mother of Bellatrix Lestrange, Andromeda Tonks, and Narcissa Malfoy
- Evan Rosier — a Death Eater who died in the First Wizarding War
- Rosier — a wizard who was one of the earliest Death Eaters
- Rosier — a woman who lived in the early 20th century
Rosier is French for "rose tree" or "rose bush" and is a common surname in Francophone areas. It is also the name of a fallen angel who was considered the patron demon of tainted love and seduction.