Short answers, pulled from the story.
Robert Devereux, 2nd Earl of Essex, was executed on the 25th of February 1601. He was beheaded inside the Tower of London after being convicted of treason for leading a failed uprising against Queen Elizabeth I's government.
Robert Devereux, 2nd Earl of Essex, was executed for treason after leading an armed rebellion against the government of Queen Elizabeth I in February 1601. He was tried before his peers on the 19th of February 1601 and found guilty of conspiring to depose the queen and seize the Crown.
Robert Devereux, 2nd Earl of Essex, led a large English army of 17,000 troops to Ireland in 1599 to suppress the Nine Years' War rebellion led by Hugh O'Neill, Earl of Tyrone. The campaign became a disaster. He avoided direct confrontation with Tyrone, dispersed his forces into garrisons, and eventually agreed to a truce that ruined his standing with the queen.
Robert Devereux, 2nd Earl of Essex, was a first cousin twice removed of Queen Elizabeth I. The link ran through his maternal great-grandmother, Mary Boleyn, a sister of Elizabeth's mother, Anne Boleyn. His mother, Lettice Knollys, was also a close friend of Elizabeth and served as her Maid of the Privy Chamber.
The Essex ring legend claims Queen Elizabeth I gave Robert Devereux, 2nd Earl of Essex, a ring after his Cadiz expedition, telling him to send it back if he ever fell into serious trouble. According to the story, Essex tried to return the ring through the Countess of Nottingham before his execution, but she withheld it. Historians such as John Lingard and Alison Weir consider the tale a fabrication.
Robert Devereux, 2nd Earl of Essex, became famous chiefly for his capture of Cadiz in June and July of 1596. The victory gave him celebrity status among London's elite. He had also fought at the Battle of Zutphen in the Spanish Netherlands in September 1586, where he was made a knight-banneret.