There were many rakshasas who had been attacking Vishvamitra's ashram, but the most vicious and dangerous among them was Tataka.
Tataka had once been a beautiful yaksha on whom Brahma bestowed the strength of a thousand elephants.
When the rishi Agastya killed her husband, Tataka vowed revenge, and Agastya in turn cursed Tataka, turning her into a monstrous rakshasi.
Enraged, Tataka and her sons, Maricha and Subahu, attacked every rishi and defiled every sacrifice.
That is why Vishvamitra brought Rama into the forest.
"You must kill Tataka and her sons!" he commanded.
"I will do as you say," Rama vowed.
Inspired by: The Ramayana (Bala Kanda).
Notes: It is Maricha who will lure Rama away from Sita, allowing Ravana to steal her. There are versions of the Ramayana where the princesses of Mithila are present at Vishvamitra's ashram, so this is when Sita and Rama meet for the first time. See Pattanaik's Sita, p. 37.