Short answers, pulled from the story.
Philip Sidney died on the 17th of October 1586 from gangrene, 26 days after being shot in the thigh at the Battle of Zutphen in the Netherlands. He was fighting for the Protestant cause against Spanish forces and was 31 years old at the time of his death.
Philip Sidney's most celebrated works are the sonnet sequence Astrophil and Stella, the prose romance The Countess of Pembroke's Arcadia, and the critical essay known as The Defence of Poetry. None of these were published during his lifetime; they circulated in manuscript and appeared in print only after his death.
Penelope Rich, born Penelope Devereux, was the inspiration for Sidney's 108-sonnet sequence Astrophil and Stella. Sidney met her in 1575; her father had reportedly planned to marry her to Sidney but died in 1576 before the arrangement was made. In 1584 she was married, apparently against her will, to Lord Rich.
At the Battle of Zutphen in 1586, Sidney was shot and lay wounded on the field. According to the famous account, he passed his water flask to another wounded soldier, saying "Thy necessity is yet greater than mine." This story became the most widely told anecdote about Sidney and was used to illustrate his gallant character.
William Shakespeare borrowed from The Countess of Pembroke's Arcadia for the Gloucester subplot of King Lear. Parts of the work were also dramatised by John Day and James Shirley. Samuel Richardson named the heroine of his first novel Pamela; or, Virtue Rewarded after Sidney's character Pamela, and a widely told story holds that King Charles I quoted lines from the Arcadia on the scaffold before his execution.
Sidney's body was interred at Old St Paul's Cathedral in London on the 16th of February 1587. The grave and its monument were destroyed in the Great Fire of London in 1666. A modern monument in the cathedral crypt lists his grave among the important ones lost to the fire.