Nicomēdes in Harpers Dictionary of Classical Antiquities (1898)
Nicomēdes I., king of Bithynia, was the eldest son of Zipoetes, whom he succeeded, B.C. 278. With the aid of the Gauls, whom he invited into Asia, he defeated and put to death his brother Zipoetes, who had for some time held the independent sovereignty of a considerable part of Bithynia. The rest of his reign appears to have been undisturbed, and under his sway Bithynia rose to a high degree of power and prosperity. He founded the city of Nicomedia, which he made the capital of his kingdom. The length of his reign is uncertain, but he probably died about 250. He was succeeded by his son Zielas.
Nicomedes I of Bithynia in Wikipedia
Nicomedes I (Greek: Nικoμήδης; 278–c. 255 BC), second king of Bithynia, was the eldest son of Zipoites, whom he succeeded on the throne in 278 BC.
He commenced his reign by putting to death two of his brothers but the third, subsequently called Zipoites II, raised an insurrection against him and succeeded in maintaining himself, for some time, in the independent sovereignty of a considerable part of Bithynia. Meanwhile, Nicomedes was threatened with an invasion from Antiochus I Soter, king of the Seleucid Empire, who had already made war upon his father, Zipoites, and, to strengthen himself against this danger, he concluded an alliance with Heraclea Pontica and shortly afterwards with Antigonus II Gonatas. The threatened attack, however, passed over with little injury. Antiochus actually invaded Bithynia but withdrew again without risking a battle.
It was more against his brother than his foreign enemies that Nicomedes now called in the assistance of more powerful auxiliaries and entered into an alliance with the Celts who, under Leonnorius and Lutarius, had arrived on the opposite side of the Bosporus and were, at this time, engaged in the siege of Byzantium, 277 BC. Having furnished them with the means of crossing into Asia he first turned the arms of his new auxiliaries against Zipoetes, whom he defeated and put to death, and thus reunited the whole of Bithynia under his dominion.
Of the events that followed we have little information. It is probable that the Celts subsequently assisted Nicomedes against Antiochus but no particulars are recorded, either of the war or the peace that terminated it. It appears, however, that Nicomedes was left in the undisturbed possession of Bithynia, which he continued to govern from this time till his death and which rose to a high degree of power and prosperity during his long and peaceful reign.
In imitation of his father, and so many others of the Greek rulers of Asia, he determined to perpetuate his own name by the foundation of a new capital and the site that he chose, in the immediate neighbourhood of the Megarian colony of Astakos, was so judiciously selected that the city of Nicomedia continued for more than six centuries to be one of the richest and most flourishing in Anatolia. The founding of Nicomedia is placed by Eusebius in 264 BC.
The duration of the reign of Nicomedes himself, after this event, is unknown but his death is assigned to around the year 255 BC. He had been twice married; by his first wife, Ditizele, a Phrygian by birth he had two sons, Prusias and Ziaelas, and a daughter, Lysandra; but his second wife, Etazeta, persuaded him to set aside his children by his first marriage and leave his crown to her offspring.
The latter were still infants at the time of his death, on which account he confided their guardianship, by his will, to the two kings, Antigonus Gonatas and Ptolemy II, together with the free cities of Heraclea, Byzantium and Cius. But, notwithstanding this precaution, his son Ziaelas quickly established himself on the throne. It is probably this Nicomedes who sought to purchase from the city of Cnidus the celebrated statue of Venus, by Praxiteles, by offering to remit the whole public debt of the city.