I've seen plenty of books published recently which still perpetuate myths about Hugh Despenser the Younger: that Edward II arranged his marriage to his (Edward's!) niece Eleanor de Clare after Despenser became his favourite; that he was nothing more than a humble knight; that he became Edward's favourite shortly after the battle of Bannockburn in 1314, or even before. I've even seen books which follow the same line as R. Perry's Edward the Second: Suddenly, at Berkeley (1988, p. 35) which makes the astonishing claim that Despenser and his father were "not members of a baronial family." Hugh Despenser the Younger was in fact the grandson of the earl and countess of Warwick and of the countess of Norfolk. Bizarre.
Hugh Despenser married Eleanor de Clare on 26 May 1306, eight years before her brother died at Bannockburn and over a year before Edward II acceded to the throne. The marriage was arranged not by Edward II but Edward I, who attended the wedding in his chapel at Westminster and paid thirty-seven pounds for minstrels to perform there, including harpers called Richard de Whiteacre and Richard de Leyland. The king gave his granddaughter almost twenty-nine pounds to buy jewels for her wedding, plus ten pounds to buy robes for her household. (Thanks to Susan Higginbotham for sending me this ref.) 
Chronicler Piers or Pierre Langtoft (died c. 1307) writes of the knighting of Edward of Caernarfon and his companions on 22 May 1306:
Three hundred knights of account in truth
Were dubbed at the cost of king Edward.
Several of the most noble were married on that occasion.
The earl of Warenne, with his newly received title,
Espoused the daughter of the count de Barre.
The earl of Arundel, in possession of his fees,
Took there the damsel whose father was named
William de Warenne, who had departed to God.
Sir Hugh son of Hugh, called Despenser,
Took there the maiden of noble kindred,
Whom Gilbert de Clare had begotten
On Joan the countess surnamed of Acres. 
Notice how Langtoft calls Despenser "of the most noble" of the nearly 300 new knights. Edward I agreed to pay Despenser the Elder a whopping £2000 for the younger Hugh's marriage, and an entry on the Patent Roll of June 1306 describes the financial arrangements made for Hugh and Eleanor: Despenser the Elder was to give them land worth £200 a year for the rest of his life. (Which in fact he didn't.) 
Edward II wrote to his Exchequer clerks regarding the dower of Eleanor's damsel Joan in March 1309, "at the request of the king's niece Eleanor le Despenser."  He gave twenty marks on 21 October 1310 to a messenger called John Chaucomb for the news he had brought to the king "respecting the Lady Eleanor le Despenser."  Queen Isabella's household book for 1311/12 still survives and has been published, with English translation, and contains at least ten references to "Lady Eleanor le Despenser."  An entry on the Close Roll of 20 April 1311 mentions "John de Berkhamstede, who has long served Eleanor le Despensere, the king's niece..."  There are numerous other entries which call Eleanor 'le Despenser' long before her husband became the king's favourite. How difficult can it possibly be for writers to check the correct date of Despenser and Eleanor's wedding, or at least notice the many instances when she is called by Despenser's name, instead of assuming that Edward II arranged their marriage in or after 1314? Even Wikipedia gets the date right on both Despenser's and Eleanor's pages, for pity's sake. It doesn't say much for authors' research when published works are sub-Wikipedia standard.
Marriage to the king of England's eldest granddaughter was a brilliant match for Despenser considering he was not set to inherit an earldom, and rather less brilliant for Eleanor, but evidently Edward I thought he was a good enough husband for her. He would hardly have paid £2000 for the marriage of a nobody who was the son of a nobody. Confusion arises, at least among people who don't do enough research, because Edward II did marry his other favourites off to Eleanor's sisters: Piers Gaveston and Hugh Audley to Margaret, Roger Damory to Elizabeth. But there is no doubt whatsoever that he had nothing to do with Despenser's marriage to Eleanor. By the time Despenser became Edward's favourite in or shortly after 1318, he'd been married to Eleanor for a dozen years, and had perhaps half a dozen children, the eldest of whom was born in 1308 or 1309. Their known children were: Hugh, Edward, Gilbert, John, Isabel, Joan, Eleanor, Margaret, Elizabeth and an unnamed boy who died young in 1321, perhaps stilborn.
Although Despenser was not of the highest rank of the nobility, he was a heck of a long way from being merely a humble knight. His mother Isabel Beauchamp was the daughter of the earl of Warwick who died in 1298, and sister of the earl of Warwick who abducted Piers Gaveston in 1312. That Despenser was the nephew of the man who abducted Edward II's first favourite is not nearly as well-known as it should be. The earl of Ulster, Richard de Burgh (c. 1259-1326) was the first cousin of Despenser's mother - their mothers Maud and Aveline FitzJohn or FitzGeoffrey were sisters. Despenser's elder half-sister Maud Chaworth, daughter of Isabel Beauchamp's first marriage to Patrick Chaworth, married Edward I's nephew Henry of Lancaster in 1296 or 1297. Hugh Despenser the Elder's mother Aline Basset (died 1281) was countess of Norfolk by her second marriage, the first wife of Roger Bigod (died 1306) who married secondly Alicia, daughter of the count of Holland and Hainault. Despenser the Elder was thus the son-in-law of the earl of Warwick and the stepson of the earl of Norfolk, not to mention an able and experienced diplomat high in favour with Edward I, and was a very long way from being the nobody some writers insist he was. (See Marc Morris's The Bigod Earls of Norfolk in the Thirteenth Century for the fascinating story of Norfolk trying to dispossess his stepson of Aline Basset's inheritance by pretending that Aline had borne him a child.) Despenser the Elder's step-grandmother Ela - the second wife of Aline Basset's father Philip - was the daughter of Henry II's illegitimate son the earl of Salisbury and countess of Warwick by her first marriage. Despenser the Younger was, through his mother, the great-great-great-grandson of the famous William Marshal, earl of Pembroke, and the great-great-grandson of Geoffrey FitzPeter, earl of Essex and of Hugh Bigod, earl of Norfolk. Yes, these are the men who were "not members of a baronial family."
Hugh Despenser the Younger was first summoned to parliament on 29 July 1314, "whereby he is held to have become Lord le Despenser."  He was appointed Edward II's chamberlain in the summer of 1318 "at the request and counsel of the magnates," and thus was not chosen by Edward himself, and continued in the position until his execution in November 1326, except for his few months in exile in 1321/22.  The later chronicler Geoffrey le Baker says that Edward was indignant at Despenser's appointment as chamberlain, as he disliked him. Whether that's true or not is hard to say, but it is certainly true is that Edward did precious little for Despenser before 1317/18.
Edward refused to hand over Despenser and his wife's share of her brother the earl of Gloucester's inheritance until November 1317, nearly three and a half years after Gloucester's death, even though Despenser went before parliament and Edward's council about half a dozen times in 1316 and 1317 to point out that Gloucester's widow could not possibly be pregnant by him and could he and his wife please, please have their rightful inheritance? From 1320, Edward II fell over himself to give Hugh Despenser anything he wanted, and his actions here demonstrate conclusively that Despenser was not yet in his favour. As late as March 1318, Edward took the county of Gwynllwg into his own hands after Despenser had persuaded its tenants to pay homage and fealty to himself instead of to Hugh Audley, the rightful owner, and ordered Despenser to withdraw from the county and the tenants to pay homage to Audley instead.  Hardly the actions of a man in the grip of an infatuation with Hugh Despenser.
Although Despenser's wife was Edward's favourite niece and Despenser's father one of the king's most loyal supporters and friends, Despenser himself wielded minimal influence at court and over the king until he took possession of his wife's share of the de Clare inheritance, and the favours he was granted were pretty trivial ones. For example, in 1313 and 1315 Despenser asked for favours on behalf of a chapel near Winchester and for permission for his brother-in-law John St Amand to re-grant two of his manors.  Grateful though the chapel and St Amand most probably were, this is a very far cry from Despenser's later supremacy at court. Edward granted Despenser the forfeited lands of two Scotsmen in June 1314 (which he never received thanks to Edward's failures in Scotland) and two wardships in October 1313 and April 1317, and gave him permission in September 1312 to hunt foxes, hares, cats and badgers but not the king's deer.  And that's about it. Before 1316 Despenser did not witness a single charter of Edward's. This stands in stark contrast to his father, who witnessed more than half of all Edward's charters between 1307 and 1314, including 98.5% of them in 1312/13 and 88.5% in 1313/14. Despenser the Younger witnessed just 5.7% of Edward's charters in 1317/18, 35.5% in 1318/19, 68.6% in 1319/20, and just under 80% in 1320/21. There's his rise to Edward's favour, right there. His position as chamberlain evidently had little to do with this, as the king's previous chamberlain John Charlton witnessed only a little over 3% of Edward's charters between 1314 and 1316, and none at all in other years.  Despenser's first big grant from Edward came in November 1317, when he received lands in South Wales "in satisfaction of 600 marks due to him for staying with the king." 
After Piers Gaveston's death in June 1312, Edward II had no male favourite for quite some time, three and a half years in fact, until numerous grants of land, money and favours from late 1315 onwards demonstrate the rise of the Oxfordshire knight Roger Damory in his affections. Damory really was little more than a humble knight, a younger son with few prospects. Hugh Audley and William Montacute were also prominent at court from 1316 to 1318. Writers who think that Despenser became Edward's favourite in about 1314 thus miss Damory, Audley and Montacute completely. The first real indication that Hugh Despenser, who as royal chamberlain spent a considerable amount of time in Edward's company, was growing close to the king comes during the siege of Berwick-on-Tweed in September 1319: the king promised to make Despenser keeper of the castle once Berwick fell. On the other hand, he also promised to make Roger Damory constable of the town, so Damory was evidently still high in Edward's favour. It was as late as 26 October 1320 when Edward finally demonstrated that he was prepared to do anything for Despenser, no matter how politically suicidal and unpopular, when he took the peninsula of Gower into his own hands, almost certainly with the intention of granting it to his favourite.  The king thus kicked off the Despenser War and the (temporary) exile of both Hugh Despensers.
That's much later than a lot of writers seem to think. I've also seen it written that Edward heaped Despenser with titles, which he didn't: Despenser was lord of Glamorgan by right of his wife, and never received any other titles. It was only after Edward's 1322 defeat of the magnates who had exiled Despenser that he bestowed numerous forfeited lands on his favourite, again much later than lots of people seem to think. It's fascinating to contemplate precisely when, why and how Edward became so infatuated with a man he'd known for most of his life and had evidently never much liked or trusted before, to what extent Despenser's machinations were responsible for this, and what the nature of their relationship was. But whatever else Hugh Despenser the Younger was - pirate, extortionist, tyrant, one of the most hated men of the Middle Ages - he certainly wasn't a humble knight who only married into the royal family because of Edward II's infatuation with him.
1) Minstrels and jewels: National Archives E 101/369/11.
2) Chronicle of Pierre de Langtoft, ed. Thomas Wright, vol. 2, pp. 368-369.
[Sir Huge le fiz Hug, Despenser appellez,
I prist la pucelle de gentil parentz,
Quele Gilbert de Clare avoit engendrez
Sur Jone la countesse de Acres surnomez.]
3) Calendar of Close Rolls 1307-1313, p. 5; Calendar of Patent Rolls 1301-1307, p. 443.
4) Calendar of Chancery Warrants 1244-1326, p. 283.
5) Frederick Devon, Issues of the Exchequer, p. 124.
6) The Household book of Queen Isabella of England, for the fifth regnal year of Edward II, 8th July 1311 to 7th July 1312, ed. F. D. Blackley and Gustav Hermansen.
7) Close Rolls 1307-1313, p. 351.
8) Complete Peerage.
9) Parliament Rolls of Medieval England.
10) Close Rolls 1313-1318, pp. 531-532.
11) Patent Rolls 1307-1313, pp. 528, 561, 571; Ibid. 1313-1317, p. 265.
12) Calendar of Documents Relating to Scotland 1307-1357, p. 69; Patent Rolls 1307-1313, p. 492; Patent Rolls 1313-1317, pp. 20, 640; Fine Rolls 1307-1319, pp. 181, 203, 223, 242, 278.
13) J. S. Hamilton, 'Charter Witness Lists for the Reign of Edward II', Fourteenth-Century England 1, ed. Nigel Saul, pp. 5, 11, 14.
14) Patent Rolls 1317-1321, p. 56.
15) Close Rolls 1318-1323, p. 268.