Step 1: Recall Ravana's family background.
In the Ramayana, Ravana is described as a powerful rakshasa king ruling over Lanka, born from the union of a sage and a rakshasi princess.
Step 2: Identify the father.
Ravana's father was the sage Vishrava, a learned Brahmin sage, and his mother was Kaikesi, a rakshasa princess, which explains Ravana's mix of scholarly and demonic traits in the epic.
Step 3: Note related family details.
Because of his father, Vishrava, Ravana is also referred to by the patronymic Raavana meaning son of Vishrava in some traditions, and this lineage links him to the sage Pulastya, who was Vishrava's father.
Final Answer: Vishrava.