Dan Gerhard Brown was born on June 22, 1964 in Exeter, New Hampshire. He has a younger sister, Valerie (born 1968) and brother, Gregory (born 1975). Brown attended Exeter's public schools until the ninth grade. He grew up on the campus of Phillips Exeter Academy, where his father, Richard G. Brown, was a teacher of mathematics and wrote textbooks from 1968 until his retirement in 1997.

In August 2005 author Lewis Perdue unsuccessfully sued Brown for plagiarism, on the basis of claimed similarity between The Da Vinci Code and his novels, The Da Vinci Legacy (1983) and Daughter of God (2000). Judge George Daniels said, in part: "A reasonable average lay observer would not conclude that The Da Vinci Code is substantially similar to Daughter of God."  In April 2006 Brown's publisher, Random House, won a copyright infringement case brought by authors Michael Baigent and Richard Leigh, who claimed that Brown stole ideas from their 1982 book Holy Blood Holy Grail for his 2003 novel The Da Vinci Code. It was in the book Holy Blood Holy Grail that Baigent, Leigh, and co-author Henry Lincoln had advanced the theory that Jesus and Mary Magdalene married and had a child and that the bloodline continues to this day. Brown apparently alluded to the two authors' names in his book. Leigh Teabing, a lead character in both the novel and the film, uses Leigh's name as the first name, and anagrammatically derives his last name from Baigent's. Mr Justice Peter Smith found in Brown's favor in the case, and as a private amusement, embedded his own Smithy code in the written judgment.  On March 28, 2007, Brown's publisher, Random House, won an appeal copyright infringement case. The Court of Appeal of England and Wales rejected the efforts from Baigent and Leigh, who became liable for paying legal expenses of nearly US$6 million.  Brown has been sued twice in U.S. Federal courts by the author Jack Dunn who claims Brown copied a huge part of his book The Vatican Boys to write The Da Vinci Code (2006-07) and Angels & Demons (2011-12). Both lawsuits were not allowed to go to a jury trial. In 2017, in London, another claim was begun against Brown by Jack Dunn who claimed that Justice was not served in the U.S. lawsuits.

Using a quote from the above article, answer the following question: why did he sue?
Daniels said, in part: "A reasonable average lay observer would not conclude that The Da Vinci Code is substantially similar to Daughter of God."