What is the name of Josh Lyman's long-time assistant?

Josh Lyman's long-time assistant is Donna Moss. Played by Janel Moloney, Donna works for Josh while he is the White House Deputy Chief of Staff during most of the early seasons of The West Wing.

Donna is far more than a conventional administrative assistant. She manages Josh's schedule, messages, and daily crises, while also questioning his assumptions and translating complicated political issues for viewers. Her quick exchanges with Josh became a recurring feature of the series, and she jokingly describes herself as the “deputy deputy chief of staff.”

Donna was initially written as a minor character with only two lines in the pilot, but Moloney's performance and chemistry with Bradley Whitford led the role to expand. Their unresolved romantic tension becomes one of the show's longest-running subplots. Donna eventually leaves Josh's office to work on political campaigns, including Bob Russell's and Matt Santos's, and later becomes chief of staff to the First Lady. Bonnie and Ginger are assistants to other staff members, while Margaret works for Leo McGarry.