WASHINGTON—Late Sunday, a group representing thousands of FBI agents told its members it was optimistic about the agency’s future, in part because its new director, Kash Patel, had assured the group he would choose a deputy from among their ranks.

Dan Bongino has been chosen as the FBI's second-in-command, a job that doesn't need Senate confirmation. Here's what to know about the Secret Service agent-turned-conservative media personality.