Agatha Harkness was one of Earth's most powerful witches and a member of New Salem who later left the colony on her own. She became a governess, tutoring children in need, though she eventually retired. But when the Fantastic Four contacted her to ask her to watch their newborn baby, Franklin, she agreed immediately when she considered who his parents were.
When the heroes first brought Franklin to her house atop Whisper Hill, she invited them in to spend the night as it was too late and too stormy for them to return home. Though once the Thing and the Human Torch had settled down, the Thing fell through a swiveling painting in his room and straight into the clutches of the Frightful Four. The evil four soon captured the rest of the Fantastic Four, but Medusa, who had been asked to join them, turned on them once she knew their plans. After a brief fight she was also restrained using the Trapster’s glue.
But the remaining three soon faced Agatha Harkness, herself, though they underestimated her. She warned them that her cat, Ebony’s, hackles were up, but the Wizard ignored her warning and attacked. The cat transformed into a massive panther and soon sent him fleeing out of the window where he smashed into a tree and was knocked unconscious. The Sandman and Trapster attacked moments later, but Agatha turned the Sandman’s body into rock and used her magic to convince the Trapster that the newly-freed Thing was a monstrous, demonic creature, wherein he fainted dead away in fright.
The rest of the Fantastic Four soon recovered as the Frightful Four’s weapons crumbled to dust minutes before, thanks to Agatha. They rushed to locate the baby and found him in Agatha’s care, sleeping soundly. Before they also went to sleep at her behest, Ben Grimm spied a book entitled Tales of Old Salem on an end table. Agatha taunted him with the possibility that she was a witch, which sent him running down the hall to his own room.
Agatha became Franklin’s permanent governess afterwards, eventually giving up her own life twice, finally at the hands of her own student: the Scarlet Witch.