The Jagrafess was a gigantic, gelatinous purple/dark pink creature similar to a slug in shape. It was sentient and its only known methods of talking seemed to consist of growls and screeches. It had a life span of about three thousand years, with sharp, vicious teeth and several vestigial eyes. Its metabolic rate, however, meant that it had to be kept at low temperatures to survive. (TV: The Long Game)
The Jagrafess was put in charge of the ersatz Fourth Great and Bountiful Human Empire in the year 199,909. Away from its home planet, only a facility like Satellite Five could produce enough cold air to sustain it. If no cold air was supplied, the Jagrafess would overheat and explode spectacularly. The heat from Floor 500, where the Jagrafess was installed, was channelled away to the rest of the station, allowing the Jagrafess to remain in a cool climate. Since the Jagrafess could not operate Satellite Five's controls, a human known only as the Editor carried out its orders.
The Ninth Doctor discovered the Fourth Great and Bountiful Human Empire was being controlled by the Jagrafess in 200,000. With the Doctor helping her realise the irregularity of the heating system, Cathica Santini Khadeni used her infospike to channel the heat back towards Floor 500, killing it by causing it to explode. (TV: The Long Game)
The Jagrafess itself was a pawn of the Daleks, part of a stratagem spanning several hundred years. After its death, the Daleks went on to other stratagems and renamed the Satellite the Game Station. (TV: The Parting of the Ways)
The Doctor would later compare the media being in control of Arkannis Major to "the thing on Satellite Five", not remembering the Jagrafess' name. (PROSE: The Stealers of Dreams) The Jagrafess was later mentioned by the Eleventh Doctor. (PROSE: The Silent Stars Go By)