Born the youngest son in a prominent family, Thomas Seymour was both well-connected and probably spoiled. His family connections allowed him to achieve high office and wield a fair amount of power in the upper ranks of English society, but his character flaws -- including taking or trying to take what was not his -- always doomed his efforts at personal success.

He was the brother of King Henry VIII's third wife, Jane Seymour. Further, as the mother to Henry's only male heir, Jane and her family became particularly influential at court and with the king himself. As a child he was, along with his sister, the Boleyn sisters, and others, sent to the court of France to attend Mary Tudor, sister of the English king. Mary was married to the French king.

His time abroad helped to inform Thomas in the ways of French culture, style, and ways of living. When his sister became queen, Henry elevated the family with titles and massive tracts of land. He also employed Thomas in the royal household and sent him on diplomatic missions abroad. Eventually he became admiral of the English fleet, charged with protecting the Channel against invasion. He was mentioned in Henry's will, and the king asked for Thomas to be elevated to the peerage.

In 1547 he was created Baron Seymour of Sudeley. Upon Henry's death, Thomas Seymour married the king's widow, Catherine Parr, and strongly pushed for a marriage between his nephew, the new King Edward VI, and the Lady Jane Grey. Also during this time he began to engage in an inappropriate relationship with his wife's stepdaughter, the Princess Elizabeth. Catherine Parr was heartbroken, and was compelled to send her beloved stepdaughter away before the relationship developed further. Less than a year later, Catherine died as a result of childbirth complications.

At this point Thomas began to behave even more irrationally, plotting to marry either Elizabeth or Lady Jane. His brother, Edward Seymour, was named Protector of the Realm during the regency of Edward VI. Thomas was clearly jealous of his brother's reputation and accomplishments, and sought to outdo him in other ways. Unfortunately, he chose illegal avenues to fame and began to involve himself in piratical activities, something which, as High Admiral, he was charged to suppress. In early 1549 he was arrested and then convicted of treason, and was executed weeks later.