In Irish folklore, a leprechaun (Irish: leipreachán) is a type of male fairy, usually taking the form of an old man who enjoys partaking in mischief. Like other fairy creatures, they have been linked to the Tuatha Dé Danann of Irish mythology.
The name leprechaun derives from the Irish word leipreachán, defined by Patrick Dinneen as “a pigmy, a sprite, a leprechaun”. The further derivation is less certain; according to most sources, the word is thought to be a corruption of Old Irish luchorpán or luchorp, from the roots lú small and corp body. The root corp, which was borrowed from the Latin corpus, attests to the early influence of Church Latin on the Irish language.  The alternative spelling leithprachán is due to the a folk etymology that would derive the word from leith half and bróg shoe, according to the frequent portrayal of the leprechaun as working on a single shoe.

Folklore
The leprechaun is said to be a solitary creature, whose principal occupation is making and mending shoes, and who enjoys practical jokes. According to Yeats, the great wealth of these fairies comes from the “treasure-crocks, buried of old in war-time”, which they have uncovered and appropriated. According to McAnally the leprechaun is the son of an “evil spirit” and a “degenerate fairy” and is “not wholly good nor wholly evil”.

In several Irish legends leprechauns have a power of hypnotism or trickery that confuses their target, either allowing the leprechaun to escape or just to play tricks on unsuspecting victims.

According to legend, if anyone keeps an eye fixed upon one, he cannot escape, but the moment the gaze is withdrawn, he vanishes

Appearance

The leprechaun originally had a different appearance depending on where in Ireland he was found.  Prior to the 20th century, it was generally agreed that the leprechaun wore red and not green. Samuel Lover, writing in the 1831 describes the leprechaun as,

… quite a beau in his dress, notwithstanding, for he wears a red square-cut coat, richly laced with gold, and inexpressible of the same, cocked hat, shoes and buckles.

According to Yeats, the solitary fairies, like the leprechaun, wear red jackets, whereas the “trooping fairies” wear green. The leprechaun’s jacket has seven rows of buttons with seven buttons in each row. On the western coast, he says, the red jacket is covered by a frieze one, and in Ulster the creature wears a cocked hat, and when he is up to anything unusually mischievous, he leaps on to a wall and spins, balancing himself on the point of the hat with his heels in the air.”

According to McAnally, “He is about three feet high, and is dressed in a little red jacket or roundabout, with red breeches buckled at the knee, gray or black stockings, and a hat, cocked in the style of a century ago, over a little, old, withered face. Round his neck is an Elizabethan ruff, and frills of lace are at his wrists. On the wild west coast, where the Atlantic winds bring almost constant rains, he dispenses with ruff and frills and wears a frieze overcoat over his pretty red suit, so that, unless on the lookout for the cocked hat, ‘ye might pass a Leprechawn on the road and never know it’s himself that’s in it at all.’” This dress could vary by region, however. In McAnally’s account, the northern leprechaun or Logheryman wore a military “red coat and white breeches”, with a “broad-brimmed, high, pointed hat”, on which he would sometimes stand upside down. The Lurigadawne of Tipperary wore “an antique slashed jacket of red, with peaks all round and a jockey cap, also sporting a sword, which he uses as a magic wand.” The Luricawne of Kerry was “a fat, pursy little fellow whose jolly round face rivals in redness the cut-a-way jacket he wears, that always has seven rows of seven buttons in each row”. The Cluricawne of Monaghan wore “a swallow-tailed evening coat of red with green vest, white breeches, black stockings,” shiny shoes, and a “long cone [hat] without a brim,” sometimes used as a weapon.

In a poem entitled The Lepracaun; or, Fairy Shoemaker, the 18th century Irish poet William Allingham describes the appearance of the leprechaun as:

…A wrinkled, wizen’d, and bearded Elf,
Spectacles stuck on his pointed nose,
Silver buckles to his hose,
Leather apron – shoe in his lap…

Some commentators accuse Allingham of leaving the legacy of the modern image of the leprechaun.

The modern image of the leprechaun is almost invariant: he is depicted as having red hair (often with a beard), wearing an emerald green frock coat.