Question: Who created Rivendell, ruled by Elrond who appears in a trilogy?

Context paragraphs:
Rivendell: Rivendell is an Elven realm in Middle-earth, a fictional world created by J. R. R. Tolkien.  It is an important location in Tolkien's legendarium, and is featured in "The Hobbit", "The Lord of the Rings", "The Silmarillion", and "Unfinished Tales".  It was established and ruled by Elrond Half-elven in the Second Age of Middle-earth (four or five thousand years before the events of "The Lord of the Rings"), and was protected by the powers of its lord and his elven ring Vilya.

Celebrían: Celebrían is a fictional character created by J. R. R. Tolkien.  She is an Elven noblewoman, the daughter of Celeborn and Galadriel, wife of Elrond, and mother of Elrohir, Elladan and Arwen.  She was called the Lady of Rivendell.  Her name means "silver crown-gift" in Sindarin (one of the languages invented by Tolkien).

Elrond: Elrond Half-elven is a fictional character in J. R. R. Tolkien's Middle-earth legendarium.  He is introduced in "The Hobbit", and plays a supporting role in "The Lord of the Rings" and "The Silmarillion".

R2-D2: R2-D2 is a fictional robot character in the "Star Wars" franchise created by George Lucas, who appears in the original trilogy, the prequel trilogy, the sequel trilogy, and Rogue One.  A small astromech droid, R2-D2 is a major character and appears in all "Star Wars" films to date.  Throughout the course of the films, he joins or supports Padmé Amidala, Anakin Skywalker, Leia Organa, Luke Skywalker, and Obi-Wan Kenobi in various points in the saga.

Hugo Weaving: Hugo Wallace Weaving (born 4 April 1960) is an English-Australian film and stage actor.  He is best known for playing Agent Smith in "The Matrix" trilogy (1999–2003), Elrond in "The Lord of the Rings" (2001–2003) and "The Hobbit" (2012–2014) film trilogies, V in "V for Vendetta" (2006), Red Skull in "" (2011) and Tom Doss in "Hacksaw Ridge" (2016).

Same-sex marriage by Circuit Court: Prior to the landmark ruling "United States v. Windsor", the constitutionality of banning same-sex marriage was upheld by the Eighth Circuit in "Citizens for Equal Protection v. Bruning".  After the "Windsor" ruling, many same-sex marriage bans were struck down by lower courts.  The Tenth, Fourth, Seventh, and Ninth circuits all ruled that same-sex marriage bans were unconstitutional.  The cases that made it to these circuit courts originated in district courts which for the most part also struck down same-sex marriage bans.  When a circuit court struck down a state's same-sex marriage ban, it did not directly strike down same-sex marriage bans in other states within the circuit.  However, it paved the way for same-sex marriage bans to be struck down in the entire circuit due to the precedent it set for district courts within the circuit to follow.  In some states, same-sex marriage was already legal before a federal circuit court ruled on the matter.  The Sixth Circuit ruled that same-sex marriage bans were not unconstitutional and reversed the district court rulings that struck down same-sex marriage bans.  Since this was the only circuit court to rule this way post-"Windsor", this created a circuit split which ultimately led to the Supreme Court of the United States deciding to resolve the issue once and for all.  They ruled that same-sex marriage bans violate the constitution in the landmark ruling "Obergefell v. Hodges" which was the consolidated case that covered each state in the Sixth Circuit.  Some circuit courts have not ruled on the constitutionality of same-sex marriage bans at all.  Many circuit courts had pending same-sex marriage cases, but decided to hold off on litigation until the Supreme Court ruled on the matter.

Aníron: "Aníron" is a song in "The Lord of the Rings" film trilogy soundtrack.  It is the theme for Aragorn and Arwen Evenstar.  "Aníron" means "I desire" in the constructed Elvish language of Sindarin.  It is featured as part of the track "The Council of Elrond" on the soundtrack album "The Lord of the Rings: The Fellowship of the Ring".  This song does not appear in Tolkien's writings; it was composed and sung by Enya, and the lyrics were written by Roma Ryan.  The song was conducted by Howard Shore and performed by the London Philharmonic Orchestra with Enya.

Celeborn: Celeborn (pronounced with a hard "c" as in "cat"; ) is a fictional character in J.R.R. Tolkien's Middle-earth legendarium.  Celeborn is an Elf, and the husband of Galadriel.  He appears in "The Lord of the Rings" as the Lord of the Galadhrim, and co-ruler along with Galadriel of Lothlórien.  He was the father of Celebrían (the wife of Elrond), and thus the grandfather of Arwen Evenstar and her older brothers Elladan and Elrohir.  He was also a kinsman of the First Age Elven King Thingol.  "Celeborn" means "(tall) silver tree" in Tolkien's invented language of Sindarin.

Khosrow IV: Khosrow IV was a Sasanian usurper who ruled briefly in 631.  Little is known about his rule, he appears to have ruled during a time of upheaval and chaos across the Sasanian Empire the 7th century has the century where Iran has plunged into its "dark ages".  He was the son of Mah-Adhur Gushnasp, who was the minister of the Sasanian Empire during the reign of Ardashir III, and Kahar-dukht, the daughter of Yazdandar, who was the son of Khosrau I.  His rule seems to coincide with other pretenders such as Hormizd VI so it is likely that he ruled a district or province rather than the Empire in its entirety.  He was killed after a few days of reign.

Somerled: Somerled (died 1164), known in Middle Irish as Somairle, Somhairle, and Somhairlidh, and in Old Norse as Sumarliði, was a mid-12th-century warlord who, through marital alliance and military conquest, rose in prominence and seized control of the Kingdom of the Isles.  Little is certain of Somerled's origins, although he appears to have belonged to a Norse–Gaelic family of some substance.  His father, GilleBride, appears to have conducted a marriage alliance with Máel Coluim mac Alaxandair, son of Alexander I of Scotland, and claimant to the Scottish throne.  Following a period of dependence upon David I of Scotland, Somerled first appears on record in 1153, when he supported kinsmen, identified as the sons of Malcolm, in their insurgence against the newly enthroned Malcolm IV of Scotland.  Following this unsuccessful uprising, Somerled appears to have turned his sights upon the kingship of the Isles, then ruled by his brother-in-law, Godred Olafsson.  Taking advantage of the latter's faltering authority, Somerled participated in a violent coup d'état, and seized half of the kingdom in 1156.  Two years later, he defeated and drove Godred from power, and Somerled ruled the entire kingdom until his death.

Supporting paragraphs: Rivendell Elrond
Answer: J. R. R. Tolkien.