Amleth, Hamlet and a Host of Characters

An 11th-12th century Danish saga entitled "Amleth" tells the tale of Feng murdering his brother, Horwendil, in order to marry Gerutha, Horwendilh's wife and Feng's sister-in-law. This causes Horwendil's son Amleth to pretend to be mad in order to save himself. The suspicious Feng sets woman and spy traps for young Amleth. Amleth eventually is sent to England with two guards carrying an execution letter, which Amleth alters to have them doom themselves. He marries the daughter of the King of England and has a son. He returns home, eventually burns the castle with his uncle's retinue then kills the uncle with his own sword. Wolves, riding horses backward, bigamy, war, an army with corpses tied up beside live men to fill out the ranks, and, most important, opportunistic and treacherous women follow.

Shakespeare had a lot to prune first.
(From Gesta Danorum of Saxo Grammaticus via Folklore and Mythology Texts webpage by D.L. Ashliman.)