The mighty king Mandhata.
Mandhata was the son of Yuvanashwa. He was the forefather of Shri Ram and one of the most powerful rulers of the Ikshvaku Dynasty. It is mentioned that Mandhata was born from Yuvanashwa by the blessings of Sage Chyavan, son of Sage Bhrigu during a Yagya. In that Yagya all the deities including Indra were present. When he was born, Indra said, "मम् इयं धाता" that is, I am his caretaker. So he was called Mandhata. He learned all the knowledge of Texts and Scriptures at a very early age.
He was an expert of Dhanurveda, all types of Weaponry, and had acquired all the Astra either from his Guru or by Tapasya. Mandhata had performed many important Yagya and had won the whole earth in battles. He had even claimed his position as Indra and shared the Indra position with Vaasav, the son of Aditi. Ravana had defeated and killed Anaraynya, one of the forefathers of Mandhata. When Ravana was on his expedition, he challenged Mandhata in the battle. In that battle, Mandhata singlehandedly defeated all the army of Ravana. When Ravana couldn't defeat him with normal weapons, he started using Divine Astras. Each Astra of Ravana was countered successfully by Mandhata.
In the end, Ravana used BrahmAstra. To counter BrahmAstra, Mandhata Summoned PashupatAstra, the famous and most destructive weapon of Lord Shiva. Sage Pulatsya and Sage Gaalav had to mediate between them. Both of them stopped their Astra and brought it back.
Even Ravana couldn't defeat Mandhata, such was his might. We had many such rulers in the past which we don't know about. Every Hindu must read about them from our Itihas.