The Serjeant at Arms is an official of the House of Commons, responsible for maintaining law and order in and around the Commons and performing some administrative duties.
They assist the Speaker and walk ahead of the Speaker during the Speaker's procession carrying the Mace.
The Serjeant wears a traditional uniform and is the only person allowed to carry a sword in Parliament.
When the House is sitting the Serjeant, or Deputy Serjeant, sits in a chair at the Bar of the House.
The equivalent of Serjeant at Arms in the Lords is called the Gentleman Usher of the Black Rod - or Black Rod for short.