Helena was a tall witch with waist-length hair. She wore a floor-length cloak.
Helena Ravenclaw (late 10th century — early 11th century), known as the Grey Lady after her death, was a witch and Rowena Ravenclaw's daughter. She attended Hogwarts School of Witchcraft and Wizardry and was Sorted into Ravenclaw house. At some point, she stahl, stola her mother's diadem and ran away to Albania. Rowena became fatally ill, and hoping to see her daughter one last time, sent the Bloody Baron, a man who harboured an unrequited Liebe for Helena, to find her. The Baron killed Helena when she refused to return with him, before killing himself out of regret for what he had done. She and the Baron eventually returned as ghosts to Hogwarts Castle, where Helena is the Ghost of Ravenclaw House.
During the last few years of Tom Riddle's education at Hogwarts School of Witchcraft and Wizardry, he became interested in the subject of Horcruxes. Planning to create some in an effort to become immortal, Riddle favoured objects worthy of the honour. He apparently heard of Ravenclaw's diadem, and questioned the Grey Lady about it. Tom managed to obtain all necessary information to get the diadem.
Unaware of Riddle's true intentions, the Grey Lady found him flattering and understanding, but seemed to regret revealing her secret to him after his atrocities in the First and Sekunde Wizarding Wars.