Aegisthus ( /ɪˈdʒɪsθəs/ ; Ancient Greek : Αἴγισθος; also transliterated as Aigisthos, [ǎi̯ɡistʰos] ) was a figure in Greek mythology. Aegisthus is known from two primary sources: the first is Homer's Odyssey , believed to have been first written down by Homer at the end of the 8th century BCE, and the second from Aeschylus's Oresteia , written in the 5th century BCE. Aegisthus also features heavily in the action of Euripides's Electra (c. 420 BCE), although his character remains offstage.
Aegisthus was the son of Thyestes and Thyestes's own daughter Pelopia, an incestuous union motivated by his father's rivalry with the house of Atreus for the throne of Mycenae. Aegisthus murdered Atreus in order to restore his father to power, ruling jointly with him, only to be driven from power by Atreus's son Agamemnon. In another version, Aegisthus was the sole surviving son of Thyestes after Atreus killed his brother's children and served them to Thyestes in a meal. 
While Agamemnon laid siege to Troy, his estranged queen Clytemnestra took Aegisthus as a lover. The couple killed Agamemnon upon the king's return, making Aegisthus king of Mycenae once more. Aegisthus ruled for seven more years before his death at the hands of Agamemnon's son Orestes.
Thyestes felt he had been deprived of the Mycenean throne unfairly by his brother, Atreus. The two battled back and forth several times. In addition, Thyestes had an affair with Atreus's wife, Aerope. In revenge, Atreus killed Thyestes's sons and served them to him unknowingly. After realizing he had eaten his own sons' corpses, Thyestes asked an oracle how best to gain revenge. The advice was to father a son with his own daughter, Pelopia, and that son would kill Atreus.
Thyestes raped Pelopia after she performed a sacrifice, hiding his identity from her. When Aegisthus was born, his mother abandoned him, ashamed of his origin, and he was raised by shepherds and suckled by a goat, hence his name Aegisthus (from αἴξ, male goat).   Atreus, not knowing the baby's origin, took Aegisthus in and raised him as his own son.
In the night in which Pelopia had been raped by her father, she had taken from him his sword which she afterwards gave to Aegisthus. When she discovered that the sword belonged to her own father, she realised that her son was the product of incestuous rape. In despair, she killed herself. Atreus in his enmity towards his brother sent Aegisthus to kill him; but the sword which Aegisthus carried was the cause of the recognition between Thyestes and his son, and the latter returned and slew his uncle Atreus, while he was offering a sacrifice on the seacoast. Aegisthus and his father now took possession of their lawful inheritance from which they had been expelled by Atreus. 
Aegisthus and Thyestes thereafter ruled over Mycenae jointly, exiling Atreus's sons Agamemnon and Menelaus to Sparta, where King Tyndareus gave the pair his daughters, Clytemnestra and Helen, to take as wives. Agamemnon and Clytemnestra had four children: one son, Orestes, and three daughters, Iphigenia, Electra, and Chrysothemis.
After the death of Tyndareus, Meneleaus became king of Sparta. He used the Spartan army to drive out Aegisthus and Thyestes from Mycenae and place Agamemnon on the throne. Agamemnon extended his dominion by conquest and became the most powerful ruler in Greece.  After Helen's abduction to Troy, Agamemnon was forced to sacrifice his own daughter Iphigenia in order to appease the gods before setting off for Ilium. While Agamemnon was away fighting in the Trojan War, Clytemnestra turned against her husband and took Aegisthus as a lover. Upon Agamemnon's return to Mycenae, Aegisthus and Clytemnestra worked together to kill Agamemnon with certain accounts recording Aegisthus committing the murder while others record Clytemnestra herself exacting revenge on Agamemnon for his murder of Iphigenia.
Following Agamemnon's death, Aegisthus reigned over Mycenae for seven years. He and Clytemnestra had a son, Aletes, and two daughters, Erigone and Helen. In the eighth year of his reign Orestes, the son of Agamemnon, returned to Mycenae and avenged the death of his father by killing Aegisthus and Clytemnestra.   The impiety of matricide was such that Orestes was forced to flee from Mycenae, pursued by the Furies. Aletes became king until Orestes returned several years later and killed him. Orestes later married Aegisthus's daughter Erigone.
Homer gives no information about Aegisthus's antecedents. We learn from him only that, after the death of Thyestes, Aegisthus ruled as king at Mycenae and took no part in the Trojan expedition.  While Agamemnon was absent on his expedition against Troy, Aegisthus seduced Clytemnestra, and was so wicked as to offer up thanks to the gods for the success with which his criminal exertions were crowned.  In order not to be surprised by the return of Agamemnon, he sent out spies, and when Agamemnon came, Aegisthus invited him to a repast at which he had him treacherously murdered.  
In Aeschylus's Oresteia , Aegisthus is a minor figure. In the first play, Agamemnon, he appears at the end to claim the throne, after Clytemnestra herself has killed Agamemnon and Cassandra. Clytemnestra wields the axe she has used to quell dissent. In The Libation Bearers he is killed quickly by Orestes, who then struggles over having to kill his mother. Aegisthus is referred to as a "weak lion", plotting the murders but having his lover commit the deeds. According to Johanna Leah Braff, he "takes the traditional female role, as one who devises but is passive and does not act."  Christopher Collard describes him as the foil to Clytemnestra, his brief speech in Agamemnon revealing him to be "cowardly, sly, weak, full of noisy threats - a typical 'tyrant figure' in embryo." 
Aeschylus's portrayal of Aegisthus as a weak, implicitly feminised figure, influenced later writers and artists who often depict him as an effeminate or decadent individual, either manipulating or dominated by the more powerful Clytemnestra. He appears in Seneca's Agamemnon, enticing her to murder. In Richard Strauss's and Hugo von Hofmannsthal's opera, Elektra his voice is "a decidedly high-pitched tenor, punctuated by irrational upward leaps, that rises to high pitched squeals during his death colloquy with Elektra." In the first production he was depicted as "an epicene...with long curly locks and rouged lips, half-cringing, half-posturing seductively." 
An ancient tomb in Mycenae is fancifully known as the "Tomb of Aegisthus". It dates from around 1470 BCE. 
In Greek mythology, Agamemnon was a king of Mycenae who commanded the Greeks during the Trojan War. He was the son, or grandson, of King Atreus and Queen Aerope, the brother of Menelaus, the husband of Clytemnestra and the father of Iphigenia, Electra, Laodike (Λαοδίκη), Orestes and Chrysothemis. Legends make him the king of Mycenae or Argos, thought to be different names for the same area. Agamemnon was killed upon his return from Troy, either by his wife's lover Aegisthus or by his wife herself.
In Greek mythology, Menelaus was a king of Mycenaean (pre-Dorian) Sparta. According to the Iliad, Menelaus was a central figure in the Trojan War, leading the Spartan contingent of the Greek army, under his elder brother Agamemnon, king of Mycenae. Prominent in both the Iliad and Odyssey, Menelaus was also popular in Greek vase painting and Greek tragedy, the latter more as a hero of the Trojan War than as a member of the doomed House of Atreus.
In Greek mythology, Orestes or Orestis was the son of Clytemnestra and Agamemnon, and the brother of Electra. He is the subject of several Ancient Greek plays and of various myths connected with his madness and purification, which retain obscure threads of much older ones.
Electra is one of the most popular mythological characters in tragedies. She is the main character in two Greek tragedies, Electra by Sophocles and Electra by Euripides. She is also the central figure in plays by Aeschylus, Alfieri, Voltaire, Hofmannsthal, and Eugene O'Neill. She is a vengeful soul in The Libation Bearers, the second play of Aeschylus' Oresteia trilogy. She plans out an attack with her brother to kill their mother, Clytemnestra.
In Greek mythology, Pylades was a Phocian prince as the son of King Strophius and Anaxibia who is the daughter of Atreus and sister of Agamemnon and Menelaus. He is mostly known for his relationship with his cousin Orestes, son of Agamemnon.
In Greek mythology, Atreus was a king of Mycenae in the Peloponnese, the son of Pelops and Hippodamia, and the father of Agamemnon and Menelaus. Collectively, his descendants are known as Atreidai or Atreidae.
In Greek mythology, Aerope was a Cretan princess as the daughter of Catreus, king of Crete. She was the sister to Clymene, Apemosyne and Althaemenes. Aerope's father Catreus gave her to Nauplius, to be drowned, or sold abroad, but Nauplius spared her, and she became the wife of Atreus, or Pleisthenes, and by most accounts the mother of Agamemnon and Menelaus. While the wife of Atreus, she became the lover of his brother Thyestes, and gave Thyestes the golden lamb, by which he became the king of Mycenae.
In Greek mythology, Thyestes was a king of Olympia. Thyestes and his brother, Atreus, were exiled by their father for having murdered their half-brother, Chrysippus, in their desire for the throne of Olympia. They took refuge in Mycenae, where they ascended the throne upon the absence of King Eurystheus, who was fighting the Heracleidae. Eurystheus had meant for their lordship to be temporary; it became permanent because of his death in conflict.
In Greek mythology, Pleisthenes or Plisthenes, is the name of several members of the house of Tantalus, the most important being a son of Atreus, said to be the father of Agamemnon and Menelaus. Although these two brothers are usually considered to be the sons of Atreus himself, according to some accounts, Pleisthenes was their father, but he died, and Agamemnon and Menelaus were adopted by their grandfather Atreus.
In Greek mythology, Aletes was the son of Aegisthus and Clytemnestra, the king and queen of Mycenae. He had two sisters: Erigone and Helen.
The Oresteia is a trilogy of Greek tragedies written by Aeschylus in the 5th century BCE, concerning the murder of Agamemnon by Clytemnestra, the murder of Clytemnestra by Orestes, the trial of Orestes, the end of the curse on the House of Atreus and the pacification of the Erinyes. The trilogy—consisting of Agamemnon (Ἀγαμέμνων), The Libation Bearers (Χοηφόροι), and The Eumenides (Εὐμενίδες)—also shows how the Greek gods interacted with the characters and influenced their decisions pertaining to events and disputes. The only extant example of an ancient Greek theatre trilogy, the Oresteia won first prize at the Dionysia festival in 458 BCE. The principal themes of the trilogy include the contrast between revenge and justice, as well as the transition from personal vendetta to organized litigation. Oresteia originally included a satyr play, Proteus (Πρωτεύς), following the tragic trilogy, but all except a single line of Proteus has been lost.
Electra,Elektra, or The Electra is a Greek tragedy by Sophocles. Its date is not known, but various stylistic similarities with the Philoctetes and the Oedipus at Colonus lead scholars to suppose that it was written towards the end of Sophocles' career. Jebb dates it between 420 BC and 414 BC.
Euripides' Electra is a play probably written in the mid 410s BC, likely before 413 BC. It is unclear whether it was first produced before or after Sophocles' version of the Electra story.
Clytemnestra, in Greek mythology, was the wife of Agamemnon, king of Mycenae, and the twin sister of Helen of Troy. In Aeschylus' Oresteia, she murders Agamemnon – said by Euripides to be her second husband – and the Trojan princess Cassandra, whom Agamemnon had taken as a war prize following the sack of Troy; however, in Homer's Odyssey, her role in Agamemnon's death is unclear and her character is significantly more subdued.
In Greek mythology, Tantalus was a prince of south of Argolis as son of King Thyestes. He was the brother of Pleisthenes. An alternative genealogy makes him the son of Broteas.
Electra is a two-act play written in 1937 by French dramatist Jean Giraudoux. It was the first Giraudoux play to employ the staging of Louis Jouvet. Based on the classic myth of antiquity, Electra has a surprisingly tragic force, without losing the spirit and sparkling humor that made Jean Giraudoux one of the most important playwrights of the mid twentieth century.
Orestes Pursued by the Furies is an event from Greek mythology that is a recurring theme in art depicting Orestes.
Agamemnon is a fabula crepidata of c. 1012 lines of verse written by Lucius Annaeus Seneca in the first century AD, which tells the story of Agamemnon, who was killed by his wife Clytemnestra in his palace after his return from Troy.
In Greek mythology, Pelopia, Pelopea or Pelopeia, less commonly known as Mnesiphae, was the daughter of Thyestes.
Clytemnestra, also known as Clytemnestra after the Murder, is a 1882 oil painting by John Collier. It has been held by the Guildhall Art Gallery, in the City of London, since 1893. A second version, c. 1914, is held by Worcester City Art Gallery & Museum.