Coronet of Rassilon

The Coronet of Rassilon was one of the many artefacts created by Rassilon. (TV: The Five Doctors) It was also known as the Matrix Circlet (TV: The Invasion of Time) and as the Crown of Rassilon. (AUDIO: Imperiatrix)

It was one of the items worn by a President of Gallifrey, being part of the "Presidential Regalia of Gallifrey". It could be used to access the Matrix, (TV: The Invasion of Time) and enabled domination over the will of others. The Fifth Doctor also deemed it a "very fetching" piece of jewelry. (TV: The Five Doctors)

History
Morbius wore the Coronet during his time as Lord President in his first incarnation. When the High Council deposed him, he was publically stripped of it (as well as of the Sash of Rassilon and the Rod of Rassilon) by then-Junior Cardinal Borusa. (PROSE: Warmonger) After he became Lord President, used the Circlet to access the Matrix during another attempt by Omega to return to his native universe. It was used to find ways to deal with Omega and find the correct wording for the execution warrant for the Fifth Doctor. (TV: Arc of Infinity)

A further regeneration of would later use the Coronet to impose his will onto the Fifth Doctor, but this was broken by the mental power of the First, Second, and Third Doctors. Borusa also paralysed the Brigadier, Sarah Jane Smith, Susan Foreman and Tegan Jovanka when he told them not to move or speak until spoken to; they were freed when Borusa was imprisoned within Rassilon's sarcophagus. (TV: The Five Doctors)

Attending the opening of a new Capitol building as Lord President, the Fifth Doctor donned the Coronet of Rassilon as part of a Presidential dress he was forced to wear. (AUDIO: Time in Office)

Pandora manifested herself through the crown when President Romana II placed it upon her head after she declared herself Imperiatrix and took it from K9 so that he could save Leela, Darkel, Narvin, her and the chapters from bombs planted in the council chambers by Antimon. (AUDIO: Imperiatrix)

Early in the War in Heaven, when Compassion visited the War King, a "golden circlet" was worn not by the King himself but by one of his advisors. When the advisor asked what "assurance" she could give of the safety of the breeding pair of pilots she demanded as payment for joining the War, she willfully misinterpreted it as a request for an assurance of the reality of the threat they all faced. Answering that imaginary question, she tapped the circlet, producing a melodic chime, and said: "what do you have for assurance? I can answer that one quite easily. As a matter of fact, I think you can answer it yourself quite easily. You know where to look. As to what you'll find there… one thing. Just one". This appeared to be a reference to the vision Lord President Umbaste experienced after entering the Caldera, which left him gibbering the word "One" over and over. (PROSE: The Book of the War)