Mestrius Plutarchus 46 - 127 better known in English as Plutarch, is regarded as one of antiquity’s greatest biographers. His Parallel Lives is a major source for biographical information on many of the ancient world’s most interesting characters.
Plutarch was born to a prominent family in Chaeronea, Boeotia, which is in modern day Greece, just outside the oracle centre of Delphi. He wrote throughout his life, including his significant extant works Parallel Lives and the Moralia.
His family was wealthy and he wrote often of his brothers and children. There is also an extant letter written to his wife Timoxena begging her not give into excessive grief at the death of their two year old daughter.
Plutarch studied mathematics and philosophy at the Academy of Athens under Ammonius from 66 to 67. Plutarch subsequently traveled widely in the Mediterranean world, including most of Greece, Alexandria, and two trips to Rome.
Despite his travels, Plutarch spent most of his life in his birthplace. He was initiated into the mysteries of the Greek god Apollo and became one of the senior priests of Apollo at the Oracle. Despite his duties at the oracle, he led an active social and civic life and produced an incredible body of writing, much of which is still extant.
Plutarch was also a magistrate in Chaeronea and he represented his home on various missions to foreign countries during his early adult years. Greece was under the aegis of Rome by Plutarch’s time and he became a Roman citizen and eventually was appointed procurator of Achaea by the Emperor Hadrian.
Plutarch died between the years 119 AD and 127 AD.

Parallel Lives

Plutarch’s best-known work is the Parallel Lives, a series of biographies of famous Greeks and Romans. The Biographies were arranged in pairs, each describing their subject’s common virtues and failings. There are 23 surviving pairs of biographies, each pair containing one Greek Life and one Roman Life. There are also four extant biographies unpaired.  A number of biographies mentioned in Plutarch’s other writings are lost.
Plutarch explains his goal was not to write chronological histories, but his intent was to exploring the influence of character — good or bad — on the lives and destinies of famous men.
Some of the characters are mythical,  Theseus and Romulus for example and some speculative such as Alcibiades and Coriolanus. In other cases, Plutarch is one of the primary sources for researchers, especially for Alexander the Great and Numa Pompilius.
"It is not histories I am writing, but lives; and in the most glorious deeds there is not always an indication of virtue of vice, indeed a small thing like a phrase or a jest often makes a greater revelation of a character than battles where thousands die."  
If there is a criticism of Plutarch’s method it is that he does, in some cases, stretch the truth or completely fabricate characteristics in order to create those parallels. For example, his biography of Pompey goes against almost all other accounts of Pompey’s character. Some of the pairings are somewhat arbitrary. For example the pairing of the Greek Nicias and Roman Crassus seems only because both were wealthy and powerful citizens who died in military battles.
Notable sections of Parallel Lives are Alexander the Great and Julius Caesar, Aristides and Cato, Demosthenes and Cicero, and Lysander and Sulla.