Nicomedes IV Philopator, was the king of Bithynia, from c. 94 BC to 75/4 BC. He was the son and successor of Nicomedes III of Bithynia and Nysa  and had a sister called Nysa. 
There is nothing known about Nicomedes 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 the king of Pontus, Mithridates the Great, one of Rome's greatest enemies during the late Republic, began harassing Bithynia's borders.
Nicomedes' brother, Socrates, assisted by Mithridates, defeated Nicomedes' army in 90 BC, and Nicomedes was forced to flee to Italy. He was restored to his throne due to Rome's influence in the region. However, the Roman Senate encouraged Nicomedes to raid Mithridates' territory, and Mithridates struck once again in 88 BC. Nicomedes fled once again to Rome.
The East was seen by the Romans as a province providing a veritable cornucopia of gold and silver. As such, two powerful Romans, Gaius Marius and the consul Lucius 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 on several occasions over the next three years, and finally in 85, Mithridates sued for peace, and was allowed to retain his kingship in Pontus after paying a heavy fine.
Nicomedes 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 Julius Caesar was an ambassador to Nicomedes' 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 homosexual relationship surfaced, leading to the disparaging title, "the Queen of Bithynia", an allegation which was made much of by Caesar's political enemies later in his life.
As one of his last acts as king of Bithynia, in 74 BC, Nicomedes bequeathed the entire kingdom of Bithynia to Rome. The Roman Senate quickly voted it as a new province. Rome's old enemy Mithridates had other plans for Bithynia, however, and Nicomedes' death and bequeathal led directly to the Third Mithridatic War.