The “Princess of Gluttony” (actual name unknown) was the self-proclaimed ruler of an unnamed region in a far corner of Equestria. She, along with her Prince, adopted the local population as their subjects and exploited them and their resources to feed the royal’s hedonistic desires.
The Prince directed many of these endeavours: insisting that the Royal Court receive the vast majority of any food produced by their makeshift kingdom, that the Princess never be washed, and that she continue to gain weight by any means necessary, no matter the detriment of her health.
So determined she constantly gain weight, the Prince insisted that prisoners would be forcibly fattened up and fed to the Princess as punishment. Later in the kingdom’s life, as both the population and food supply dwindled, this decree was extended to any subjects that did not serve a useful function to the Princess or Prince.
As their kingdom dwindled to their last few subjects, the Prince sent most of those remaining to locate a magical artefact that could multiply the amount of adipose within a pony’s body. He subsequently fed this to the Princess, causing her to rapidly grow in size multiple times over, crushing what remained of her kingdom and subjects.
The background of the Princess and Prince is unknown, other than that neither were alicorns nor true members of royalty. It is similarly unknown how they successfully installed themselves as the rulers of a region of Equestria.
It can be assumed that both the Princess and Prince were hedonists interested in extreme levels of weight gain, likely being in a feeder and feedee relationship long before the establishment of their faux kingdom.
Their actions would indicate that they were happy to indulge these interests at the expense of ethics, morals, or care for the well-being of themselves and others.
The Princess greatly enjoys eating and glutting herself, as well as bragging about her grand scale and beauty. She would occasionally flex her sovereign authority over others but usually left the Prince to command their subjects on her behalf.
The Prince doted upon the Princess constantly, frequently servicing her physically and pointedly never leaving her side. He handled many of the actual administrative functions required of royalty whilst simultaneously finding new means of fattening up the Princess to ever larger extremes.
Even relatively early in her rule, the Princess had come to weigh in the realm of dozens of tons. At the Prince’s insistance, she remained unwashed during her reign, causing her body and the area surrounding her to pool with sweat, slobber and detritus. The air around her was hot, humid and smelly.
She sat upright on a makeshift throne in the ruins of an old castle, where servants would feed her and meet her other needs.
The Prince was also heavily obese, to the degree of being functionally immobile. He normally sat either next to the Princess on his own makeshift throne or lay upon her numerous rolls. If he needed to move, he would command the unicorns of the court to levitate him to his desired position.
The Princess continued to gain weight rapidly, eventually growing too immense to fit within the throne room. After being fed the adipose-duplication gem, her mass swelled by several orders of magnitude, smothering the entirety of her kingdom and, eventually, all of Equestria.
The Princess's most carnal desire.
Poor hygiene and health issues persistently go unaddressed.
A means to an end.