What secret military organization is Riley Finn part of?

Riley Finn is part of the secret military organization known as the Initiative.

The Initiative is a covert U.S. government operation introduced during Buffy the Vampire Slayer’s fourth season. Based beneath UC Sunnydale, it studies, captures, and experiments on vampires and demons. Riley initially hides his military identity while posing as a college student and teaching assistant, which allows him to maintain a seemingly ordinary relationship with Buffy.

Riley serves under Professor Maggie Walsh and works with fellow Initiative soldiers such as Forrest Gates and Graham Miller. Buffy eventually discovers that Riley is a commando, and she becomes involved with the organization herself. The Initiative’s methods become increasingly disturbing, especially its experimentation and its plan to create the cybernetic demon Adam.

The Initiative is sometimes confused with the Watchers’ Council, but the two groups are distinct. The Council trains and guides Slayers, whereas the Initiative is a modern military and scientific project focused on supernatural threats.