King of England at the time was Richard II. Henry's father was the king's cousin (Henry senior was the son of John of Gaunt, younger brother of Richard II's father, Edward the Black prince.) Henry senior took part in a revolt against Richard, which resulted in his exile in 1398.
At that point, Richard took the twelve-year-old Henry under his wing, taking him to Ireland. A year later, his grandfather John of Gaunt died and the Lancastrian rebellion overthrew Richard and put Henry's father on the throne as Henry IV. Young Henry was now the eldest son of the reigning king, and was named heir apparent, Prince of Wales, and Duke of Lancaster. He also became Duke of Cornwall, Earl of Chester and Duke of Aquitaine.
In 1400 he was named Sheriff of Cornwall and put in charge of part of the military (note that he is about fourteen years old). In 1403 he led an English army to fight Owain Glendower (previously mentioned here). At the battle of Shrewsbury in 1403 against Henry Percy (immortalized as "Hotspur" in Shakespeare's Henry IV, Part 1), an arrow was embedded in the left side of our Henry's face.
This would have been dire for any soldier, but the king's son was going to receive the best care. The royal physician treated it with honey as a natural antiseptic, and developed a tool to extract the embedded arrowhead before flushing the wound with alcohol. The patient survived with impressive scars that proved his battle experience (although you'll note the absence of scars in the portrait above).
That physician was John Bradmore, and is too interesting a character to not stop and talk about him next.
