The elements of revenge tragedy in Thomas Kyd's The Spanish Tragedy are significant both in terms of the performance of this play in its own right and in terms of the fact that Kyd's play was a major source for Shakespeare when he wrote The Tragedy of Hamlet, the Prince of Denmark. Though The Spanish Tragedy does not have the reputation and fame of Hamlet, without the unique violence and the abject goriness of the plot and stage direction of Kyd's play, Hamlet may not exist.
The basics of revenge tragedy require a crime with a victim (in the case of Kyd's play, Andrea), and an avenging interested party who wreaks havoc on the criminals (Andrea's father). Kyd also employs the supernatural, the ghost of Andrea, at the very start of the play, disorienting the audience from the beginning. Shakespeare pays homage to Kyd when he writes in a part for King Hamlet's ghost, who also walks the earth having been murdered, and when the prince and son avenges the death of the king, his father.
Some scholars argue that Shakespeare borrowed the best aspects of Kyd's tragedy and improved upon them, like the figure of the ghost and the plot line. Other scholars, however, see The Spanish Tragedy as a stand-alone, an innovative work of literature and drama that changed theatre forever.