David Sloan, most often referred to as simply Sloan, was a security guard for billionaire Whitney Vance. He worked for Vance for approximately 25 years. When Vance hired Trident Security to provide additional protection, he kept Sloan as his personal bodyguard.
In early October 2016, he became peripherally involved in his employer's efforts to locate his heir. Vance asked Harry Bosch, not Sloan, to find whether he had fathered a child. When Vance believed he was dying he told Sloan about the assignment he had given Bosch and he asked Sloan to assist. However, Bosch was operating on Vance's original instructions to communicate with no one else. Thus, Sloan was forced to observe and aid Bosch without detection. In addition, Sloan was aware that Bosch was being monitored by Trident for less benevolent purposes.
After Vance died under suspicious circumstances, the search for Vance's heir took on new intensity. When Bosch located Vibiana Veracruz, Sloan watched her building to make sure she was safe. Bosch eventually realized that Sloan was one of the good guys.