Algernon Sidney, British philosopher (probable) (died 1683)

Algernon Sidney or Sydney was an English politician, republican political theorist and colonel. A member of the middle part of the Long Parliament and commissioner of the trial of King Charles I of England, he opposed the king's execution. Sidney was later charged with plotting against Charles II, in part based on his most famous work, Discourses Concerning Government, which was used by the prosecution as a witness at his trial. He was executed for treason. After his death, Sidney was revered as a "Whig patriot—hero and martyr".

January 15 is the 15th day of the year in the Gregorian calendar; 350 days remain until the end of the year.