John Lackland was an Angevin king of England (1199-1216 AD) and was brother to his predecessor, Richard I (who made him Count of Mortain). 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 the 12-year-old Isabella daughter of Aymer Taillefer, Count of Angouleme, with whom he had 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.
To be fair to him, he appears to have been the first English king to create an administration in the modern style -- with the Exchequer at Westminster, a Chancery there, as well as one with his own mobile Court, and (later in his reign) a system for gathering cash moneys at regional treasuries, with the central Treasury simply receiving notes of what was where, rather than physicially moving the silver pennies up and down the country.
He was noted for owning his own bath, and having it taken round with him (in an age where bathing, in water, was thought possibly life-threatening); he appears to have been the first king to import sugar, to have founded the English navy, by establishing gallies at strategic locations, as well as founding Portsmouth, and he is the first king to own a dressing gown, so much so that the recorders have to invent a description for it.