Over the years, the Green Man has been linked to several other folkloric figures which have some elements in common (although many of the purported links have since been shown to be spurious, or at least unlikely):

Jack-in-the-Green:

Jack-in-the-Green and other Green Men in the May Day Parade in Hastings, Sussex, England (Source)

A trickster character in traditional English May Day parades from the mid-18th Century onwards, represented by a man covered in a cone-shaped mass of foliage and vegetation. Although it largely fell out of popularity in the 19th Century (when it was largely replaced by the May Queen), it has seen a resurgence in recent years in May Day parades in many towns in southern England, including Hastings (see picture at right), Knutsford, Rochester, Bristol, Oxford, Ilfracombe, etc.

Green George:

A leaf-covered young man portrayed in medieval Mummer’s plays and Eastern European parades as an accomplice of St. George, or perhaps as a representation of St. George himself. In many legends, from Russia to Greece to Britain, St. George was also associated with the colour green, and is believed to have undergone death and resurrection.

John Barleycorn:

A character in an old English folksong, which personifies the cereal crop barley (important in the production of beer and whiskey, as well as in breads and soups) as a man whose life story corresponds to the various stages of barley cultivation, down to his death and re-birth each spring.

Puck (Robin Goodfellow):

A lusty and mischievous nature sprite or fairy, often used to personify the spirit of the land, and often represented as a Pan-like cloven-hoofed figure with small horns. Robin Goodfellow was the name of one such sprite, as immortalized in Shakespeare’s "A Midsummer Night’s Dream".

Robin Hood:

Although best known as the heroic, bow-wielding outlaw of English folklore since the 14th Century, along with his green-garbed band of Merry Men and the beautiful and virtuous Maid Marian, Robin Hood (originally a contraction of Robin of the Wood) was also traditionally seen as a protector of the old ways and of the woods and forests, and was a particularly popular figure in medieval May Day games and plays from the 16th to 17th Century.

Woodwose (Wild Man) by Hans Holbein the Younger (in British Museum) (Source)

Woodwose (Wild Man of the Woods):

A mythical figure found throughout Europe (and particularly popular in Germany and Switzerland), the wild man was usually shown as a naked, hairy figure armed with a wooden club, often with vegetation woven (or caught) in his hair (see picture at right). As a folklore character, he represented freedom, the wilderness and the very edges of civilized society.

The Green Knight:

Immortalized in the 14th Century English poem "Sir Gawain and the Green Knight", but probably based on a much earlier Irish tale, the Green Knight is portrayed as a mysterious and immortal green warrior (green from his clothes to his hair and skin, all but his red eyes), who challenges the honour of the Arthurian knight Sir Gawain. He has been variously associated with the Green Man, the Devil, even Christ.

Oak King / Holly King:

Folklore figures representing the dual aspects of a male Earth deity, endlessly battling each other as the seasons turn. The Oak King is in the ascendant in the summer half of the year, starting at the Spring Equinox (reaching the height of his powers at Midsummer), while the Holly King rules in the winter, starting at the Autumn Equinox (becoming fully dominant at Yule). In some versions, the two wax and wane in power throughout the year, ruling in tandem without conflict.

Herne the Hunter:

A shadowy, wild, stag-antlered folklore figure possibly dating back to Celtic or Saxon times, but only definitively recorded since the 15th Century and more commonly since the 18th and 19th Century. His ghost is said to haunt Windsor Forest, but his origins in prehistory may be connected with the male fertility/nature power, similar to the horned Celtic deity Cernunnos.

Ents:

The giant tree-herders and carers of the forests and the natural world in J.R.R. Tolkein’s “The Lord of the Rings”. Tolkein envisaged ents as wise and ancient tree-like figures with bushy, mossy beards and deep penetrating eyes, living in the primeval forest of Fangorn.