|Can't you tell I'm a giant douche?|
Seymour's sister Jane caught the eye of King Henry VIII as his relationship with Ann Boleyn fell apart, primarily due to her inability to give him a male heir. He married Jane 11 days after Ann's execution. Henry seems to have truly loved Jane, at least insofar as he was capable. She gave him his long-awaited male heir, Prince Edward (the future King Edward VI). Unfortunately, she died from complications of childbirth some two weeks later. Both of Jane's brothers were given powerful positions at court. The elder brother, Edward, was the more responsible and capable of the two, and was one of Henry's privy councilors. Thomas was never granted a councilorship by Henry, who seems to have realized he was a jackass.
Like a lot of good-looking jackasses, he managed to capture the attention of an otherwise lovely, respectable, and classy lady, Catherine Parr, whose attraction to Seymour seems to have been her only major flaw. She was one of the richest widows in England. They began a flirtation that was a great frustration to her friends and advisers. Seymour - either because he loved her or because of her fortune - proposed marriage. Unfortunately, Henry VIII had also noticed Catherine and proposed marriage. As a religious reformer, she felt God had called her to this position. Henry had been backsliding toward Catholicism ever since his break with Rome. She hoped to continue to sway him toward more radical Protestant reform, and even got herself into trouble a few times over it (fascinating tales that must be told elsewhere). With a heavy heart, she rejected Seymour's proposal and accepted Henry's.
Henry then sent Seymour to the continent to manage some parts of his disastrous and costly military campaigns in France. Seymour's bravery meant he met with a few successes, capturing two castles under the command of Sir John Wallop (pack a Wallop?). Otherwise, he was not particularly successful, failing in an important mission to recruit German mercenaries to serve Henry.
Returning to England shortly before Henry's death, Seymour was miffed that he was not on the Privy Council, and resentful that his brother Edward was high in the king's favor. He was determined to weasel his way into the royal family, expressing an interest in marrying either of Henry's daughters (Mary and Elizabeth). Nothing came of this, which surprised no one but Seymour.
Then Henry died, leaving Seymour's older brother Edward as "Lord Protector" for the child King Edward VI. Seymour was made a privy councilor, but this did not satisfy his ambition. He was given a few titles and appointments as a sort of consolation prize. Nevertheless, Thomas was consumed with jealousy of his older brother and constantly sought to undermine his influence over the young king.
Henry's death left Catherine Parr vast wealth and the freedom to marry again. Seymour swooped in and the two were married secretly, quite soon after the king's death. Seymour and Parr moved to his estates in the country. They were made protectors of Princess Elizabeth, who Seymour liked. A lot. When she was 14 years old, he began deeply inappropriate behavior toward her that probably amounted to full-on sexual abuse. However, it is unknown to what degree Elizabeth may or may not have been victimized. A strong-willed young lady faced with attention from a good-looking man, she may not have put up much resistance. All that was acknowledged publicly was that he would "romp" with her, tickle her, "slappe her behinde as she lay abed" and other things. It is even said Parr joined in a few of these "romps." Whatever happened between them, when Parr became pregnant by Seymour (her first child), she became deeply concerned over his behavior with Elizabeth and sent her away to live elsewhere. But then Parr herself died, and Seymour attempted to reconnect with Elizabeth. Already quite astute despite her years, Elizabeth took great pains to avoid him (this lends credence to the belief that she was a victim of sexual abuse, not a willing partner in their "romps").
Frustrated in his attempt to marry Elizabeth, Seymour began to secretly exercise influence over the young King Edward, using his vast wealth to give the king a generous allowance. The king was utterly reliant on others for pocket money, and this enabled him to give gifts and feel more king-like and adult. Seymour tried to cajole Edward into making him his personal governor, but this came to nothing. Finally, Seymour openly attempted to persuade the king to curtail his brother's power, which, again, came to naught. The young King Edward, in fact, seems to have held little respect for either of his Seymour uncles, preferring instead the counsel of Catherine Parr's brother, who he referred to tellingly as his "honest uncle" to distinguish him from the Seymours.
Seymour became increasingly more vocal in criticizing his elder brother and calling his policies into question. Seymour was the nominal "lord admiral" of the British fleet, whom he unwisely tried to enroll in a possible rebellion. Failing this, he negotiated with pirates on the western coasts who it was his job to keep at bay. All of this became too suspicious, and the privy council moved to order his arrest. But, despite being treated shamefully by his little brother, Edward Seymour, the Lord Protector, called a council so that Thomas could try to explain himself. This would have probably saved his life, but he never showed up to the hearing.
Soon after, in a staggering display of jackassery, Seymour, perhaps slightly unhinged, attempted to sneak into King Edward's bedchambers. We'll never know why, but it was considered most likely at the time that he was attempting to spirit the young king away, so that he could physically control the royal person and make a bid for power. Like the jackass he was, Seymour failed to realize or remember that the king routinely slept with several dogs. A spaniel barked at Seymour and he shot it. He was suddenly surrounded by palace guards, and being caught outside the king's bedchamber with a loaded gun was too much to explain away. There was no longer anything his big brother could do for him - Seymour was arrested the next day and charged with 33 counts of treason. He was executed within the month, his estates and wealth confiscated by the crown, and his daughter Mary left a destitute orphan.
A byproduct of all this is that the great men of the realm came to know Elizabeth first-hand. All of Seymour's associates were ruthlessly questioned, including Elizabeth, to see who was complicit in his treason. Although she was not first in line to succeed Edward if he died, she was in line, and her association with Seymour placed her under suspicion. During relentless questioning, the sordid details of Seymour's guardianship of her came to light, though Elizabeth is believed to have downplayed this to avoid embarrassment. During her questioning, the council was reportedly impressed with her poise, personal magnetism, and "polite defiance." She was removed from all suspicion, and made a few contacts who would serve her well when she did become queen.
So, for not realizing his own limitations, for his inability to be content with the incredible good fortune that repeatedly fell into his lap, for molesting a 14-year-old princess, for being stupid enough to think he could foment rebellion, and for grossly bungling his attempt to kidnap the young king, Seymour is, indeed, a true Jackass of History.