Borusa's first High Council

Lord President Borusa's first High Council was the administration that dealt with the Second Omega Crisis. High Chancellor Thalia, Castellan Jerricho, Cardinal Zorac and Councillor Hedin composed the Inner Council. (TV: Arc of Infinity; PROSE: A Brief History of Time Lords)

A Gallifreyan historian later described this incarnation of Borusa as "quite ineffectual", with Thalia and Zorac being "just as unimpressive". He described Jerricho as "not a team player" and Hedin more favourably as a "man of learning with centuries of public service" who was "respected by all". He described the administration as a whole as one "rife with plotting and manoeuvring for political advantage". (PROSE: A Brief History of Time Lords)

Origins
The beginning of Borusa's term as Lord President and subsequent formation of his High Council was a complicated series of events, confused greatly by the Fourth Doctor's stint as President.

Upon returning to Gallifrey, the Doctor was forced to invoke Article 17 of the Constitution of the Time Lords to avoid being executed for the assassination of the 406th President. The clause was a "guarantee of liberty" and meant that he had put himself forward as a candidate in the presidential election, alongside Goth. Goth was eventually discovered as the true assassin, under the influence of, and was killed in the process. The Doctor left Gallifrey to continue his travels after this but with no other legitimate candidate he was effectively President-elect. (TV: The Deadly Assassin)

Left without a leader, the Fourth Doctor's High Council ratified Borusa's appointment to Chancellor, an act the Doctor later claimed was illegal without his approval. (TV: The Invasion of Time) Realising the one thing they didn't have in the President's absence was supreme authority, the Council renamed itself the Supreme Council before it "wriggled its way around the technicalities" to nominate Borusa as Acting President. (PROSE: A Brief History of Time Lords)

The Doctor then unexpectedly returned to claim his right to be invested as the 407th President and oversaw the Sontaran invasion of Gallifrey. (TV: The Invasion of Time) According to one account, the Doctor gave up the presidency before he left again which allowed Borusa to be formally invested as President with the Supreme Council changing its name back to the High Council. (PROSE: A Brief History of Time Lords) According to another account, Borusa served as Acting President for "aeons" more after the Doctor departed again and was officially inducted as President sometime after the Krikkitman crisis. (PROSE: Doctor Who and the Krikkitmen)

The official history stored in the Bureau of Ancient Records stated that after Goth's death, Borusa became Chancellor and Acting President "by popular acclaim" until he could be confirmed as President by election. (PROSE: A Brief History of Time Lords)

Term in office
Whatever the circumstances of its beginnings, Borusa's High Council was the first to include the Castellan among its rank, with the holder of the position, the first being Jerricho, even gaining a place on the Inner Council. (PROSE: A Brief History of Time Lords)

Borusa eventually regenerated into a new incarnation. After the Death Zone was reactivated, (TV: The Five Doctors) Thalia and Zorac were sent by Borusa to investigate. They died, potentially only moments after entering the Zone, (PROSE: A Brief History of Time Lords) after being struck by bursts of psychic energy converted into elemental weaponry fired by Rassilon from the astral plane of the Matrix. (PROSE: The Legacy of Gallifrey)

Thalia was succeeded as Chancellor by Flavia, who was classified as a member of Borusa's final High Council. (PROSE: A Brief History of Time Lords)