Detective Sean Raley is a fictional character featured in Richard Castle's Nikki Heat series of books and is based on his and Kate Beckett's colleague at the 12th precinct Detective Kevin Ryan. Raley is a member of Nikki Heat's squad and is partnered with Detective Ochoa, who is based on Ryan's partner Detective Javier Esposito.
Like his alter-ego, he is unmarried and often the butt of Heat and Ochoa's teasing. However unlike Ryan, he is not in a long-term relationship.
His expertise lies in technology and videos to the extent that Nikki calls him the King of All Surveillance Media.