An LB exists at the Threshold of two states; this gives LBs both wisdom and the ability to instruct, while also rendering them dangerous and uncanny. Centaurs are often LBs. In classical Mythology, the centaur Chiron was the Mentor of heroes like Hercules, while his coeval Nessus was a Villain whose intelligence enabled him to enact Vengeance on Hercules from beyond the grave. Centaurs are also often seen as in Bondage to their animal natures – hence prone to drunkenness and rape. Many other LBs are in bondage, limited by their double nature to an essentially passive or catalytic role and often physically confined to a particular area, or mentally limited to particular kinds of discourse. They are not capable of change or growth – indeed, their double nature may be the product of a specific act of Metamorphosis interrupted at a halfway point; they may as a result be figures of pathos.
An LB can be both dead and alive, like Gandalf in the later stages of J R R Tolkien's The Lord of the Rings (1954-1955), or both animal and human, like the centaurs, or both animal and intelligent, like many Dragons, or both animal and vegetable, like the Ents in LOTR, or both Good and Evil, or an androgyne, or existing in a perverse relationship to past and future, like T H White's Merlin in The Once and Future King (omni 1958), or existing outside time altogether at the hinge of the year, like the Christmas Ghosts in Charles Dickens's A Christmas Carol (1843). Gods become LBs when they dwell in the world of humanity – Odin is an obvious example (and also often a Trickster). Harlequins (see Commedia dell'Arte) are often LBs.
LBs may instruct by their very existence rather than as mentors; the Green Man, whether mobile or a sessile Foliate Head, instructs humanity in its rootedness in Nature and the rhythms of Nature, even if he does not engage in direct interaction of an instructive kind, as in Sir Gawain and the Green Knight (circa 1370) (see Gawain). The Face of Glory is both divine and demonic, both full and empty; again, it stands as a sign of the voracity of intellectual and creative joy.
A distinction needs to be drawn between LBs as plot functions and full-blown LBs. The latter are comparatively rare in Heroic Fantasies and Template fantasies. Ningauble of the Seven Eyes and Sheelba of the Eyeless Face, in Fritz Leiber's Fafhrd and the Gray Mouser series, have most of the aspects and roles of LBs but exist in plots where they are merely part of the Template. Similarly, the undead Mycroft who advises Glen Cook's eponymous detective in the Garrett series exists at the threshold of life and death, and is uncanny, but his role as Garrett's mentor is to solve his cases rather than change his life. Dark Lords and their henchpersons are often both alive and dead, as are a variety of lesser Villains – like Suraklin in Barbara Hambly's The Silicon Mage (1988) – who have liminality but are not LBs. The same can be said of most Vampires and Werewolves.
Liminality is often seen as a dangerous state. Angier, in Christopher Priest's Technofantasy The Prestige (1995), is as a result of Nikola Tesla's teleportation machine simultaneously alive and dead; he is a conjurer (see Magicians) whose tricks are more than an appearance – he is at risk for stretching the margins of Reality. Wizards who turn into animals (see Shapeshifters) are at risk of losing their identity and becoming permanently and irrevocably beasts. In Robin Hobb's (Megan Lindholm's) The Farseer Trilogy, mental communication with animal companions is correctly seen as dangerous because potentially blurring the distinction between animal and human; condemned for this, the character Fitz escapes via a Night Journey in which he is doubly liminal, both animal and human and both alive and dead.
Protagonists often acquire a measure of liminality in the course of their adventures but by definition cannot be an LB in their own story, though two or more principals may serve as LBs to each other, as with Dracula and Mina in Bram Stoker's Dracula (1992) (see Dracula Movies). Covenant, in Stephen Donaldson's The Second Chronicles of Thomas Covenant the Unbeliever, serves as portal, mentor and source of the uncanny in the adventures of his co-protagonist Linden Avery. Neil Gaiman's Sandman and Death Graphic Novels, by contrast, deal in large measure with the private lives of characters – Death, Dream, Desire, etc. – who are occasionally LBs in the lives of their liminal siblings, as well as in those of the human and divine characters with whom they interact.
In John Crowley's Little, Big (1981), Alice is instructed by the LB Grandfather Trout – a shapeshifted victim of punitive metamorphosis – while herself acting as an LB to her husband Smoky Barnable. Paradoxically, it is Smoky's single nature, inability to change and consequent death that make the replacement of the Faerie in which he was unable quite ever to believe by his wife and family a progress rather than merely a stage of a Cycle. Where the earlier Faerie was uncanny and irresponsible, its replacements are chastened by his loss. [RK]