Rhesus (Greek: Ῥῆσος) is an Athenian tragedy transmitted in the corpus of Euripides, though its authorship has been disputed since ancient times. It is based on the 10th book of the Iliad, in which Odysseus and Diomedes kill the Trojan spy Dolon and raid the Trojan camp.
Free online texts
Gutenberg : Rhesus, translated by Gilbert Murray (1913). Multiple formats.
Internet Archive: Rhesus, verse translation by Gilbert Murray. Multiple formats.
Internet Classics Archive: Rhesus, HTML and TXT formats.
Loebulus: L009 - Euripides -- Euripides I: Iphigenia at Aulis. Rhesus. Hecuba. The Daughters of Troy. Helen. Greek and English parallel text. Loeb edition, PDF format.
Poetry in Translation: Rhesus, translated by George Theodoridis. Multiple formats.
University of Adelaide (Internet Archive): Rhesus, translated by E.P. Coleridge. Multiple formats.
Gutenberg: Euripides and His Age, by Gilbert Murray.
History of Ancient Greece: Early Euripides, podcast by Ryan Stitt.
Wikipedia: Rhesus (play)
The Great Conversation: Further reading at Tom's Learning Notes
Homer: The Iliad
A.E. Haigh: The Tragic Drama of the Greeks (1896).
Ancient Greek resources: Learn to read Greek classics in the original.