Question: The Heroes of Olympus is a pentalogy of adventure, mythological fiction and fantasy novels by American author Rick Riordan that collectively form a sequel series to the Percy Jackson & the Olympians series, a pentalogy of adventure and mythological fiction books written by which American author ?
Context: Perseus "Percy" Jackson is a fictional character, the title character and narrator of Rick Riordan's "Percy Jackson & the Olympians" series.  He is also one of seven main protagonists of the sequel series "The Heroes of Olympus", appearing in every book except "The Lost Hero," and appears in the ongoing "Trials of Apollo" series, making him one of the few characters to appear in all three series of the Camp Half-Blood chronicles.  He has also been a narrator and protagonist in Riordan's Greco-Roman/Egyptian crossover stories, part of the "Demigods and Magicians" collection.  The character serves as the narrator in "Percy Jackson's Greek Gods" and "Percy Jackson's Greek Heroes", also by Rick Riordan. Percy Jackson & the Olympians, often shortened to Percy Jackson, is a pentalogy of adventure and mythological fiction books written by American author Rick Riordan, and the first book series in the Camp Half-Blood Chronicles.  Five supplementary books, along with three graphic novels, have also been released.  More than 45 million copies of the books have been sold in more than 35 countries. Richard Russell Riordan Jr. ( ; born June 5, 1964), better known as Rick Riordan, is an American author.  He is known for writing the "Percy Jackson & the Olympians" series, about a twelve-year-old boy who discovers he is a son of Poseidon.  His books have been translated into 42 languages and sold more than 30 million copies in the US.  Twentieth Century Fox has adapted the first two books of his Percy Jackson series as part of a series of films.  His books have spawned related media, such as graphic novels and short story collections. Camp Half-Blood Chronicles is a media franchise created by author Rick Riordan, encompassing three five-part novel series, three short-story collections, two myth anthology books, a stand-alone short story, an essay collection, a guide, four graphic novels, two films, a video game, a musical, and other media.  Set in the modern world, it focuses on groups of demi-god teenagers, and features many characters from Greek and Roman mythology.  The first series, "Percy Jackson & the Olympians", follows the adventures of a teen named Percy Jackson at a summer camp for Greek demigods.  The second series, "The Heroes of Olympus", introduces several more lead characters and a second camp for Roman demigods.  The third series, "The Trials of Apollo", follows the now-mortal god Apollo, with appearances by many characters from the first and second series. The Blood of Olympus is a young adult novel written by American author Rick Riordan and is the fifth and final book in "The Heroes of Olympus" series.  It was released on October 7, 2014.  The seven demigods of the Prophecy of Seven—Percy Jackson, Annabeth Chase, Jason Grace, Leo Valdez, Piper McLean, Hazel Levesque, and Frank Zhang—go on their final adventure to defeat Gaea while Nico di Angelo, Reyna Avila Ramírez-Arellano, and Coach Gleeson Hedge attempt to bring the Athena Parthenos to Camp Half-Blood in order to prevent a war between the Roman and Greek demigods.  The chapters are written from the perspectives of Jason, Piper, Leo, Reyna, and Nico, making it the first time in the series that someone other than one of the seven demigods of the prophecy is the viewpoint character.  It is the second time that Percy appears without being a viewpoint character (first being in "The Lost Hero"). The Kane Chronicles is a trilogy of adventure and Egyptian mythological fiction books written by American author Rick Riordan.  The series is set in the same universe as Riordan's "Percy Jackson & the Olympians", "The Heroes of Olympus", and "Magnus Chase and the Gods of Asgard". Seven Wonders is a pentalogy of children's fantasy, adventure and mythological fiction books written by American author Peter Lerangis.  It is based on Greek mythology and set around the Seven Wonders of the Ancient World.  Jack McKinley discovers a secret organization on a hidden island, and becomes the leader of a mission to retrieve seven lost magical orbs.  As Jack and his three friends realize their lives are at stake, they have no choice but to accept the quest and embark on the challenge. The Trials of Apollo is a series of fantasy adventure mythological fiction novels written by American author Rick Riordan that collectively form a sequel to the "Heroes of Olympus" series.  The first book in the series, "The Hidden Oracle", was released on May 3, 2016.  The second book in the series, "The Dark Prophecy", was released on May 2, 2017. The Heroes of Olympus is a pentalogy of adventure, mythological fiction and fantasy novels by American author Rick Riordan that collectively form a sequel series to the "Percy Jackson & the Olympians" series.  This series details a conflict between Greek and Roman demigods and Gaea, the earth goddess.  Riordan introduces Roman mythology into his sequel series as well as several new characters.  The first book of the series, "The Lost Hero", was published on October 12, 2010.  The final entry in the series, "The Blood of Olympus", was published on October 7, 2014. The Lightning Thief is a 2005 fantasy-adventure novel based on Greek mythology, the first young adult novel written by American author Rick Riordan.  It is the first novel in the "Percy Jackson & the Olympians" series, which charts the adventures of modern-day twelve-year-old Percy Jackson as he discovers he is a demigod, the son of a mortal woman and the Greek god Poseidon.  Percy and his friends Annabeth Chase and Grover Underwood go on a quest to prevent a war between the gods Zeus, Poseidon, and Hades.
Answer: Rick Riordan