John Lackland was an Angevin king of England (1199-1216 AD) and was brother to his predecessor, Richard I. He had many failures, losing his French territories (hence the nickname "Lackland" or "Sans Terre"), being excommunicated by the Pope and being forced to ratify the Magna Carta. He is also known as the Prince John of the Robin Hood stories (and almost certainly was responsible for trying to filch Richard's ransom money) and didn't have a good reputation with his populace. However, he did manage to maintain a number of the reforms instituted by his father, Henry II.
He married twice. First to Isabella (also known, variously, as Avice or Advisa, Hawise, Joan and Eleanor), daughter of William, Earl of Gloucester, with no children. Second to Isabella daughter of Aymer Taillefer, Count of Angouleme, with children Henry, Richard, Isabella & Eleanor. He also had an illegitimate daughter, Joan, whom he married to Llewelyn the Great of Wales, thereby initiating the English claim to sovereignty over Wales.
Indeed John seems to have had some problem with his seed-sowing. History also knows of a son Geoffrey, who died in 1205 old enough to be made lord of Perche and placed in nominal command of a small expedition into Poitou on John's behalf. Another son named John appears to have become a clerk in the see of Lincoln, and there was a Henry fitz-Roy who was given the Cornish lands of Robert Fitz Walter, married a minor heiress, and lived well into Henry III's reign, acknowledged as the King's brother, as well as a Richard (apparently born to a sister of Earl WIlliam de Warren) who was to marry a prominent heiress, Rohese of Dover, and become lord of the castle and barony of Chilham in Kent.
He was a loser if there ever was one. Not only was he plagued with the problems both he and Richard I created, but near the end of his life, his personal belongings were misplaced in a soggy bog called the Wash, between Norfolk and Lincolnshire. Hereafter, he is called "The King who lost his clothes in the Wash". It was reported that the Crown jewels also went down, but none of the locals ever reported finding them.