Puck is a mischievous pre-Christian nature spirit, a "woodwose" in the archetype of the Horned God. The pagan trickster was reimagined in Old English puca (cf. Old Norse puki, Christianized as "devil") as a kind of half-tamed woodland sprite, leading folk astray with echoes and lights in nighttime woodlands (like the Celtic/French "White Ladies", the Dames Blanches), or coming into the farmstead and souring milk in the churn. Significantly for such a place-spirit or genius, the Old English word occurs mainly in placenames, which strongly suggests that the Puca was older in the landscape of Britain than the language itself. Since the O.E.D. debates whether the origin is Germanic (Old Norse puki) or Celtic (Welsh pwcca and Irish pooka), Puck's origins may lie on an even deeper language layer, before the Celtic and North Germanic language families split.
Since, if you "speak of the Devil" he will appear, Puck's euphemistic "disguised" name is "Robin Goodfellow" or "Hobgoblin," in which "Hob" may substitute for "Rob" or may simply refer to the "goblin of the hearth" or hob.
If you had the knack, Puck might do minor housework for you, quick fine needlework or butter-churning, which could be undone in a moment by his knavish tricks, if you fell out of favor with him: "Those that Hob-goblin call you, and sweet Puck, You do their work, and they shall have good luck" said one of Shakespeare's fairies. Shakespeare's characterization of "shrewd and knavish" Puck in A Midsummer Night's Dream may have revived flagging interest in Puck.
An early 17th century broadside ballad, "The Mad Merry Pranks of Robin Goodfellow", which is so deft and literate it has been taken for the work of Ben Jonson, describes Puck/Robin Goodfellow as the emissary of Oberon, the faery king, inspiring night-terrors in old women but also carding their wool while they sleep, leading travellers astray, taking the shape of animals, blowing out the candles to kiss the girls in the darkness, twitching off their bedclothes, or making them fall out of bed on the cold floor, tattling secrets, and changing babes in cradles with elflings. All his work is done by moonlight, and his mocking, echoing laugh is "Ho ho ho!"
Milton, in L'Allegro tells "how the drudging Goblin swet/ To earn his cream-bowle duly set" by threshing a week's worth of grain in a night, and then, "stretch'd out all the chimney's length,/Basks at the fire his hairy strength." Milton's Puck is not small and sprightly, but nearer to a Green Man or a hairy woodwose. For followers of neo-Pagan imagery, sometimes the influence of Pan imagery has now given Puck the hindquarters and cloven hooves of a goat. He may even have small horns. In Ireland "puck" is said to be sometimes used for "goat".
Puck's trademark laugh in the early ballads is "Ho ho ho." In modern mythology, the "merry old elf" who works with magical swiftness unseen in the night, who can "descry each thing that's done beneath the moone," whom we propitiate with a glass of milk, lest he put lumps of coal in the stockings we hang by the hob with care, and whose trademark laugh is "Ho ho ho" —is Santa Claus.
In Rudyard Kipling's Puck of Pook's Hill (1906), Puck, the last of the People of the Hills and "the oldest thing in England," charms the children Dan and Una with a collection of tales and visitors out of England's past.