Nicomedes IV Philopator (Greek: Νικομήδης) was the king of Bithynia from c. 94 BC to 74 BC. He was the first son and successor of Nicomedes III of Bithynia and Nysa and had a sister called Nysa.
There is nothing known about Nicomedes IV's birth or the years before he became king. However, his reign began at the death of his father. The first few years of his kingship were relatively peaceful, but soon King Mithridates VI of Pontus (the maternal grand-uncle of Nicomedes IV), one of Rome's greatest enemies during the late Republic, began harassing Bithynia's borders.
Nicomedes IV's brother, Socrates Chrestus, assisted by Mithridates VI, defeated Nicomedes IV's army in 90 BC, and Nicomedes IV was forced to flee to Italy. He was restored to his throne by Manius Aquillius due to Rome's influence in the region. However, Aquillius encouraged Nicomedes IV to raid Mithridates VI's territory, prompting Mithridates VI to retaliate again in 88 BC. Nicomedes IV fled once again to Rome.
The East was seen by the Romans as a province providing an abundance of gold and silver. As such, two powerful Romans, Gaius Marius and the ConsulLucius Cornelius Sulla aimed at command in the region. Sulla fled the intrigues of Rome to Anatolia, where he commenced the First Mithridatic War. Sulla fought Mithridates VI on several occasions over the next three years, and finally in 85 BC, Mithridates VI sued for peace, and was allowed to retain his kingship in Pontus after paying a heavy fine.
Nicomedes IV was restored to his throne in Bithynia in 84 BC. The years that followed were relatively peaceful, though Bithynia came more and more under the control of Rome. In 80 BC, young Gaius Julius Caesar was an ambassador to Nicomedes IV's court. Caesar was sent to raise a fleet using Bithynia's resources, but he dallied so long with the King that a rumor of a sexual relationship between the two men surfaced, leading to the disparaging title for Caesar, "the Queen of Bithynia", an allegation which Caesar's political enemies made use of later in his life. A popular quip at the time ran: "Gallias Caesar subegit, Caesarem Nicomedes, (Caesar laid the Gauls low, Nicomedes laid Caesar low), suggesting that Caesar was the receiving partner in the relationship.
As one of his last acts as king of Bithynia, in 74 BC, Nicomedes IV bequeathed the entire kingdom of Bithynia to Rome. The Roman Senate quickly voted it as a new province. Rome's old enemy Mithridates VI had other plans for Bithynia, however, and Nicomedes IV's death and bequeathal led directly to the Third Mithridatic War.