Plutarch (c. 45–125 CE) is an ancient Greek biographer who used material that is no longer available to us for his biographies. His two main works are called Parallel Lives and Moralia. The Parallel Lives compare a Greek and a Roman with a focus on how the character of the famous person influenced his life. Some of the 19 completely parallel lives are a stretch and many of the characters are ones we would consider mythological. Other parallel lives have lost one of their parallels.
The Romans made many copies of the Lives and Plutarch has been popular since. Shakespeare, for instance, closely used Plutarch in creating his tragedy of Antony and Cleopatra.