Pontius Pilate [Pontii Pilat]
The name Bulgakov chooses, "Pontii," is unusual for Russian, which usually refers to him by the adjectival form "Pontiiskii."
Pilate was the Roman procurator of the province of Judea from 26-36 AD. The procurator was the highest Roman authority in the province, subject to governor-general of the province of Syria.
Pilate's name may be derived from L "pilus" meaning "spear" He appears in the Bible, in various Apocrypha, and in the historical works of Philo of Alexandria (Leg. ad Caj. 38) and Flavius Josephus (Antiq. 18:3, 4 and Bell. II:9, 2-4). A legend cited in the encyclopedia holds that he appears once each year on Mount Pilatus in Switzerland.
In Chapter 26 Pilate is called The son of an astrologer-king and a miller's daughter, Pila-This appears to come from one of the many medieval legends about Pilate. One from Mainz mentions him as the son of the astrologer Ata and miller's daughter Pila. (I. F. Belza. Genealogiia "Mastera i Margarity" 173-74) Galinskaia considers that Bulgakov learned of this legend from G. A. Müller, Pontius Pilatus, der fünfte Prokurator von Judäa und Richter Jesu von Nasareth, Stuttgart 1888 (Galinskaia I L. Zagadki izvestnykh knig. M 1986, 73). Other possible medieval sources include a Latin poem "Pilate" that was translated into Russian, or a Russian work from the 15th century "A Journey to Florence". He is mentioned in many apocryphal accounts. The historical Pilate was prefect of Judea from AD 26-36. After the Samaritans complained about him and the governor of Syria was angered at him he was sent back to Rome to see the Emperor Tiberius. Tiberius died before Pilate arrived back and his fate is subsequently unclear though there are hints of suicide. The reference to poison comes from apocryphal accounts.
A very good page from the Ecole Initiative explains almost everything we need to know about the historical Pilate.
The Catholic Encyclopedia page on Pontius Pilate is also informative.