In the Hindu epic the Ramayana, Prahastha was a powerful rakshasa warrior, chief commander of Ravana's army of Lanka and son of Ravana. In his next birth Prahastha was reborn as Purochana in the Mahabharata as Duryodhana's trusted aide and who was responsible for the Lakshagraha incident. In both his births he has been the minister of the Villains of the time. This is also a clear instance of Swabhava traividya of souls.
Prahastha leads Ravana's army in the wars against Yama, Kubera and the Devas, and the Asuras and Daityas, through which Ravana establishes his sovereignty over the three worlds. He also leads the initial Lankan response to the invasion led by Rama, Lakshmana, Sugriva and the Vanara army.
Prahastha was the younger brother of Indrajit, who died at the hands of Lakshmana on the first day of the Battle between the forces of Rama and Ravana on the Soil of Lanka.
Prahastha Killed several important warriors of the Sugriva's army was actually proving to be real threat to the army of Rama, so Lakshmana had to move in to the rescue of the beleaguered army, who was suffering at the hands of the Prahastha (quoted directly from the Tulasidas Ramayana). Even Valmiki has gone in to describe that the ruthless warrior Prahastha was, and Lakshmana had to use all the celestial weapons to kill this warrior.