Thomas Stanley, 1st Earl of Derby in the context of Earl of Surrey

The Battle of Bosworth or Bosworth Field (/ˈbɒzwərθ/ BOZ-wərth) was the last significant battle of the Wars of the Roses, the civil war between the houses of Lancaster and York that extended across England and Wales in the latter half of the 15th century. Fought on 22 August 1485, the battle was won by an alliance of Lancastrians and disaffected Yorkists. Their leader Henry Tudor, Earl of Richmond, became the first Welsh monarch of England from the Tudor dynasty by his victory and subsequent marriage to the de facto Yorkist heiress, Elizabeth of York. His opponent Richard III, the last king of the House of York, was killed during the battle, the last English monarch to fall in battle. Historians consider Bosworth Field to mark the end of the Plantagenet dynasty, making it one of the defining moments of English history.

Richard's reign began in 1483 when he ascended the throne after his twelve-year-old nephew, Edward V, was declared illegitimate, likely at Richard’s instigation. The boy and his younger brother Richard soon disappeared, and their fate remains a mystery. Across the English Channel Henry Tudor, a descendant of the greatly diminished House of Lancaster, seized on Richard's difficulties and laid claim to the throne. Henry's first attempt to invade England in 1483 foundered in a storm, but his second arrived unopposed on 7 August 1485 on the south-west coast of Wales. Marching inland, Henry gathered support as he made for London. Richard hurriedly mustered his troops and intercepted Henry's army near Ambion Hill, south of the town of Market Bosworth in Leicestershire. Lord Stanley and Sir William Stanley also brought a force to the battlefield, but held back while they decided which side it would be most advantageous to support, initially lending only four knights to Henry's cause; these were: Sir Robert Tunstall, Sir John Savage (nephew of Lord Stanley), Sir Hugh Persall and Sir Humphrey Stanley. Sir John Savage was placed in command of the left flank of Henry's army.

Demise of the Crown is the legal term in the United Kingdom and the other Commonwealth realms for the transfer of the Crown upon the death or abdication of the monarch. The Crown transfers automatically to the monarch's heir. The concept evolved in the kingdom of England, and was continued in Great Britain and then the United Kingdom. The concept also became part of the constitutions of the British colonies, and was continued in the constitutions of the Commonwealth realms, until modified within those realms.

Originally, the demise of the Crown in England had significant legal effects: individuals who had been appointed to office by the deceased monarch lost their positions; if Parliament was sitting, it automatically dissolved; and actions in the royal courts automatically discontinued and had to be re-started. Almost all of these legal effects have been abolished by statutes of the British Parliament and the parliaments of the Commonwealth realms, so that the demise of the Crown no longer has much legal significance.

Sir William Stanley KG (c. 1435 – 16 February 1495) was an English soldier and the younger brother of Thomas Stanley, 1st Earl of Derby. Stanley fought with his troops in several battles of the Wars of the Roses.

Sir John Savage, KG, KB, PC (1444–1492), was an English knight of the Savage family, who was a noted military commander of the late 15th-century. Savage most notably fought at the Battle of Bosworth Field in 1485, where he commanded the left flank of the Tudor (Lancastrian) army to victory and is said to have personally slain the Duke of Norfolk in single combat. Earlier in the Wars of the Roses, Savage had been a supporter and friend of the Yorkist King Edward IV, fighting alongside him and helping him to victories at the Battle of Barnet in April 1471 and the Battle of Tewkesbury the following month. He returned to active military service in 1482 when he joined the invasion of Scotland led by the King's brother Richard, Duke of Gloucester, where the Duke made him a Knight banneret.

However, following the death of Edward and the Duke of Gloucester's ascension to the throne as Richard III, the Savage family was viewed with suspicion due to their familial connection to the Stanleys, who were in turn connected to the Tudors. Consequently, Savage was one of the prominent figures who invited Henry Tudor to invade England in 1485, a struggle which culminated in the Battle of Bosworth Field. After his victory, Henry Tudor received the circlet of Richard from Savage's uncle, Lord Stanley, and was crowned King of England on the field of battle, taking the throne as Henry VII of England.