Short answers, pulled from the story.
Apollodorus of Damascus was an architect and engineer from Roman Syria who flourished during the 2nd century AD. He served as the favoured architect of the emperor Trajan and is credited with introducing several Eastern innovations to Roman Imperial architecture, including making the dome a standard element. He is one of the few architects from antiquity whose name has survived.
Apollodorus designed Trajan's Forum, Trajan's Markets, the Temple of Trajan, and Trajan's Column in Rome. Outside Rome, he built Trajan's Bridge across the Danube, the Alconétar Bridge over the Tagus in Spain, the triumphal arch at Benevento, the Arch of Trajan at Ancona, and Trajan's Trophy near Adamclisi in Romania.
Apollodorus was born in Damascus, in the province of Roman Syria. Modern scholars describe him variously as Nabatean, Hellenized Nabatean, Arab, or Greek; neither Cassius Dio nor Procopius specified his ethnic origins. Some scholars argue the name Apollodorus is a Hellenized form of the Nabataean names Abdal or Abodat.
Cassius Dio reports that Apollodorus offended the emperor Hadrian by mocking Hadrian's architectural designs, leading to his banishment and death. Many modern historians doubt this account. The historian Jona Lendering argues it is unlikely because Hadrian faced more serious threats early in his reign and apparently acted on the criticism Apollodorus made.
Apollodorus wrote a technical treatise on military siege engines called the Poliorcetica, dedicated to an unnamed emperor most likely identified as Trajan. He also authored several other technical treatises, though details of their content are not widely preserved.
Apollodorus likely first encountered Trajan in Syria, where he began his career as a military engineer. When Trajan was consul in 91 AD, he summoned Apollodorus to Rome, and the architect made the journey after his twentieth birthday. He later accompanied Trajan during the Second Dacian War in 105 AD.