I have a report: the Spanish have located the Fountain of Youth. I will not have some melancholy Spanish Monarch—a Catholic—gain eternal life!!
~ King George to Jack Sparrow.
George Augustus (or King George ll) is the overarching antagonist of the Pirates of the Caribbean film series. He was the unseen overarching antagonist of The Curse of the Black Pearl, Dead Man's Chest and At World's End, right before he made an appearance in On Stranger Tides as the overarching antagonist and serves as a background antagonist in the fifth film Dead Men Tell No Tale.
King George was shown to be a greedy, arrogant and power-hungry tyrant, as he plans to expand the British Empire through all means necessary, such as ridding the Seven Seas of the Brethren Court that would leave the East India Trading Company in charge for international trade of the Empire. He is also shown to be prejudiced towards the Spanish and Catholics, as he sternly states that he won't let the Fountain of Youth fall into their hands to achieve eternal life.
The Curse of the Black Pearl
King George was first mentioned in the first film, where he ordered the extermination of all pirates in the island of Isla de Muerta following the death of Hector Barbossa and the arrest of Barbossa's crew.
Dead Man's Chest
The King was mentioned again in the second film, where he provided signed Letters of Marque for Lord Cutler Beckett after the latter took possession of the heart of the notorious pirate Davy Jones. As it turns out, the King plans to use Jones and his crew to rid the world of a pirate council (known as the Brethren Court) and control the Seven Seas for his true purposes of international trade.
At World's End
The King was mentioned again in the third film, where he happily appointed Beckett as commander of a Royal Navy armada to attack and eliminate the Brethren Court at all costs. However, this all failed when Captain Jack Sparrow and his crew (along with a revived Barbossa) managed to kill Jones to free his crew from Beckett's control, and they team up together to kill Beckett by sinking down his ship for good. With both Beckett and Jones killed, the armada is forced to retreat from the seas, leaving the King's plans for conquest in complete vain.
On Stranger Tides
The King finally made his appearance in On Stranger Tides when Joshamee Gibbs and Sparrow were caught by the guards when the courtroom audience yelled. The guards take them to St. James' Palace, where they placed Jack on the chair and the king finally meets him in person. King George tells Sparrow of his next plan to find the Fountain of Youth before the King Ferdinand VI of Spain does. It is also revealed that Blackbeard was a former privateer of King George before he became a pirate, as he too intends to seek out the Fountain for eternal life. As such, King George intends of having Sparrow lead an expedition to find the Fountain, but Sparrow escapes, leaving an annoyed King George to appoint Barbossa (who became a privateer following Beckett and Jones' deaths) to lead the expedition. Little did King George knew that King Ferdinand actually intends to destroy the Fountain rather than using it to gain eternal life and that Barbossa only became a privateer to exact his revenge on Blackbeard for taking away the Black Pearl. Eventually, the Spanish forces (led by Ferdinand's trusted agent The Spaniard) succeeded in destroying the Fountain while the British troops are killed, except for Barbossa, who reverted back to piracy following Blackbeard's death. It is unknown what happened to King George afterward.
Dead Men Tell No Tales
The King doesn't appear, nor is mentioned in Dead Men Tell No Tales, but is referenced when Lieutenant Scarfield hears of a powerful object called the Trident of Poseidon, known for controlling the creatures of the sea and creating strong thunderstorms and tidal waves. As such, Scarfield plans to obtain the Trident for the King so that the British Empire can take control of the Seven Seas, but in the end, Scarfield and his crew end up being killed by Armando Salazar and his undead crew, who would later meet the same fate following the destruction of the Trident.
Despite being mentioned in the first three films and making a cameo appearance in the fourth film, King George is clearly the overarching villain of the first four films of the series, as Davy Jones and Lord Cutler Beckett were answering to him during their battle against the Brethren Court; even Hector Barbossa and Blackbeard used to serve him as privateers before their turn to piracy.
King George is one of the two historical monarchs (the other is King Ferdinand VI) to appear in the Pirates of the Caribbean film series.
He most likely didn't appear in the fifth film Dead Men Tell No Tales due to actor Richard Griffiths' death in 2013. However, it's easily deduced that Scarfield wanted to get the Trident of Poseidon for him.