Aeschylus (UK: , US: ; Greek: Aiskhulos Aiskhulos; Ancient Greek: [ais.khy.los]; c. 525/524 - c. 456/455 BC) was an ancient Greek tragedian. He is often described as the father of tragedy. Academics' knowledge of the genre begins with his work, and understanding of earlier tragedies is largely based on inferences from his surviving plays.

One hallmark of Aeschylean dramaturgy appears to have been his tendency to write connected trilogies, in which each play serves as a chapter in a continuous dramatic narrative. The Oresteia is the only extant example of this type of connected trilogy, but there is evidence that Aeschylus often wrote such trilogies. The comic satyr plays that follow his trilogies also drew upon stories derived from myths.  For example, the Oresteia's satyr play Proteus treated the story of Menelaus' detour in Egypt on his way home from the Trojan War. Based on the evidence provided by a catalogue of Aeschylean play titles, scholia, and play fragments recorded by later authors, it is assumed that three other of his extant plays were components of connected trilogies: Seven against Thebes being the final play in an Oedipus trilogy, and The Suppliants and Prometheus Bound each being the first play in a Danaid trilogy and Prometheus trilogy, respectively (see below). Scholars have moreover suggested several completely lost trilogies derived from known play titles. A number of these trilogies treated myths surrounding the Trojan War. One, collectively called the Achilleis, comprised the titles Myrmidons, Nereids and Phrygians (alternately, The Ransoming of Hector).  Another trilogy apparently recounts the entry of the Trojan ally Memnon into the war, and his death at the hands of Achilles (Memnon and The Weighing of Souls being two components of the trilogy); The Award of the Arms, The Phrygian Women, and The Salaminian Women suggest a trilogy about the madness and subsequent suicide of the Greek hero Ajax; Aeschylus also seems to have written about Odysseus' return to Ithaca after the war (including his killing of his wife Penelope's suitors and its consequences) in a trilogy consisting of The Soul-raisers, Penelope and The Bone-gatherers. Other suggested trilogies touched on the myth of Jason and the Argonauts (Argo, Lemnian Women, Hypsipyle); the life of Perseus (The Net-draggers, Polydektes, Phorkides); the birth and exploits of Dionysus (Semele, Bacchae, Pentheus); and the aftermath of the war portrayed in Seven against Thebes (Eleusinians, Argives (or Argive Women), Sons of the Seven).  Aeschylus continued his emphasis on the polis with The Suppliants in 463 BC (Hiketides), which pays tribute to the democratic undercurrents running through Athens in advance of the establishment of a democratic government in 461. In the play, the Danaids, the fifty daughters of Danaus, founder of Argos, flee a forced marriage to their cousins in Egypt. They turn to King Pelasgus of Argos for protection, but Pelasgus refuses until the people of Argos weigh in on the decision, a distinctly democratic move on the part of the king. The people decide that the Danaids deserve protection, and they are allowed within the walls of Argos despite Egyptian protests.  The 1952 publication of Oxyrhynchus Papyrus 2256 fr. 3 confirmed a long-assumed (because of The Suppliants' cliffhanger ending) Danaid trilogy, whose constituent plays are generally agreed to be The Suppliants, The Egyptians and The Danaids. A plausible reconstruction of the trilogy's last two-thirds runs thus: In The Egyptians, the Argive-Egyptian war threatened in the first play has transpired. During the course of the war, King Pelasgus has been killed, and Danaus rules Argos. He negotiates a peace settlement with Aegyptus, as a condition of which, his fifty daughters will marry the fifty sons of Aegyptus. Danaus secretly informs his daughters of an oracle predicting that one of his sons-in-law would kill him; he therefore orders the Danaids to murder their husbands on their wedding night. His daughters agree. The Danaids would open the day after the wedding.  In short order, it is revealed that forty-nine of the Danaids killed their husbands as ordered; Hypermnestra, however, loved her husband Lynceus, and thus spared his life and helped him to escape. Angered by his daughter's disobedience, Danaus orders her imprisonment and, possibly, her execution. In the trilogy's climax and denouement, Lynceus reveals himself to Danaus, and kills him (thus fulfilling the oracle). He and Hypermnestra will establish a ruling dynasty in Argos. The other forty-nine Danaids are absolved of their murderous crime, and married off to unspecified Argive men. The satyr play following this trilogy was titled Amymone, after one of the Danaids.  In addition to these six works, a seventh tragedy, Prometheus Bound, is attributed to Aeschylus by ancient authorities. Since the late 19th century, however, scholars have increasingly doubted this ascription, largely on stylistic grounds. Its production date is also in dispute, with theories ranging from the 480s BC to as late as the 410s.  The play consists mostly of static dialogue, as throughout the play the Titan Prometheus is bound to a rock as punishment from the Olympian Zeus for providing fire to humans. The god Hephaestus, the Titan Oceanus, and the chorus of Oceanids all express sympathy for Prometheus' plight. Prometheus meets Io, a fellow victim of Zeus' cruelty; and prophesies her future travels, revealing that one of her descendants will free Prometheus. The play closes with Zeus sending Prometheus into the abyss because Prometheus refuses to divulge the secret of a potential marriage that could prove Zeus' downfall.  The Prometheus Bound appears to have been the first play in a trilogy called the Prometheia. In the second play, Prometheus Unbound, Heracles frees Prometheus from his chains and kills the eagle that had been sent daily to eat Prometheus' perpetually regenerating liver. Perhaps foreshadowing his eventual reconciliation with Prometheus, we learn that Zeus has released the other Titans whom he imprisoned at the conclusion of the Titanomachy.  In the trilogy's conclusion, Prometheus the Fire-Bringer, it appears that the Titan finally warns Zeus not to sleep with the sea nymph Thetis, for she is fated to give birth to a son greater than the father. Not wishing to be overthrown, Zeus marries Thetis off to the mortal Peleus; the product of that union is Achilles, Greek hero of the Trojan War. After reconciling with Prometheus, Zeus probably inaugurates a festival in his honor at Athens.

Answer the following question by taking a quote from the article: What is the Prometheus Bound?
The Suppliants and Prometheus Bound each being the first play in a Danaid trilogy and Prometheus trilogy,