Augustus (aka Gaius Octavius or C. Julius Caesar Octavianus) became the first Roman emperor mainly because he had been adopted by Julius Caesar. Caesar is often referred to as Augustus' uncle.
Gaius Octavius (Augustus), born September 23, 63 B.C., was the son of Octavius, a praetor from Velitrae, and Atia, the daughter of Julius Caesar's sister Julia. When Caesar went to Spain to fight the Pompeians in 45 B.C., Gaius Octavius went with him. Caesar arranging the schedule in advance, named Gaius Octavius Master of the Horse for 43 or 42 B.C. Caesar died in 44 B.C. and in his will adopted Gaius Octavius. Octavius took the name C. Julius Caesar Octavianus at this point.
Before he was assassinated, Julius Caesar named his grand-nephew Octavius as heir, but Octavius did not know of it until Caesar's death. He then took the name C. Julius Caesar Octavianus or Octavian (or simply Caesar), which he kept until he was named Imperator Caesar Augustus on January 16, 17 B.C.
Instead of following Caesar's example and making himself dictator, Octavian in 27 BC founded the principate, a system of monarchy headed by an emperor holding power for life. His powers were hidden behind constitutional forms, and he took the name Augustus meaning 'lofty' or 'serene'. Nevertheless, he retained ultimate control of all aspects of the Roman state, with the army under his direct command.
Relations deteriorated between Octavian and Antony in 32 B.C. when Antony renounced his wife Octavia in favor of Cleopatra.
Augustus adopted Tiberius, his wife's son, in A.D. 4 and gave him proconsular and tribunician power. He married his heir to his daughter Julia. In 13, Augustus made Tiberius co-regent.
Augustus died in 14 A.D. and was succeeded by his son-in-law Tiberius.
