George III
In the later part of his life, George suffered from recurrent mental illness, which was eventually permanent. Although it has since been suggested that he suffered from a genetic blood disease, porphyria, the cause of his illness is not certain. After a final relapse in 1810, a regency was established, and George's eldest son, George, Prince of Wales, ruled as Prince Regent. On George III's death, the Prince Regent succeeded his father as George IV.