Ms. Siren is a siren and a teacher at Monster High. She hosts Voice Training, one of Monster High's night classes. Ms. Siren was originally mentioned in Holt's 'Basic' diary as "a siren who gives voice lessons", but she received a name in the May 2013 edition of the Monster High magazine.
In Ancient Greek mythology, the sirens were the companions of Persephone before she was abducted by Hades. Persephone's mother, Demeter, either made them birdlike and gave them wings to go look for her daughter and their friend or cursed them to such shape due to their failure to protect Persephone. The sirens were a group of two to five creatures, depending on the myth, and had the ability to sing in such a way that any male human hearing them was compelled to come to them. Again depending on the myth, the how and why differs. In some versions, the sirens' song is actually their call for Persephone and the effect on male humans and their subsequent drowning is accidental. In others, the now-monstrous sirens sing specifically to lure sailors and eat them.
Due to being creatures of the sea, the modern Western world has conflated sirens with mermaids. Monster High itself has an example of each interpretation: Melody Carver is a birdlike siren and the Create-A-Monster siren is fishlike. Which version Ms. Siren is is currently unknown.