Demigod

Demigods, are considered the first rung on the ladder of the gods. Note that while Exarchs are called demigods, and they are quite similar to Demigods in some ways, they are not quite the same thing. Demigods, are true immortal deities and capable of granting spells A demigod typically has only a handful of clerics and roughly 300 to 3,000 worshipers that typically pray to a deity of such power.

A demipower is a god that that either has just risen to godhood, just returned from the dead, suffered a loss of divine power or shares a part of their portfolio with a god of greater power. For example Finder Wyvernspur is an example of a mortal that rose to the rank of demipower. Moander is an example of a once powerful god that returned from the dead as a demipower. . Jergal is an example of a Greater deity at the time of Netheril but reduced himself to the level of a demipower. And both Savras and Velsharoon are examples of demigods that share their portfolios with gods of greater power, Azuth and Mystra.

Due to their very natures, demigods represent a very narrow and restricted ideal or aspect of existence. This means only a certain group of mortals will consider the demigod suitable for worship, until either the ideals that the demigod embodies become more popular or the demigod is given or takes the portfolios of other deities.

Demigod Abilities
A demigod may create and control a small realm (generally within one of the Outer Planes) that can be shaped and controlled as the demigod wishes. Additionally, the demigod has a small ability to shape reality in regard to his or her portfolio as it relates to mortal life, become extraordinary in some skill related to his or her portfolio, and extend his or her senses to a mile away from an avatar or any holy sites dedicated to him or her.

Faerûnian Demigods

 * Deep Duerra
 * Finder Wyvernspur
 * Garagos
 * Gargauth
 * Gwaeron Windstrom
 * Haela Brightaxe
 * Hoar
 * Jergal
 * Kiaransalee
 * Laogzed
 * Lurue
 * Nobanion
 * Red Knight
 * Savras
 * Sebek
 * Selvetarm
 * Sharess
 * Shiallia
 * Siamorphe
 * Ulutiu
 * Valkur
 * Vaprak
 * Velsharoon

Demigod Discombobulation
In every edition of D&D except 4th, demigods have been the lowest rank of power of the divine god scale. They are true gods, just the weakest of the true gods. In 3rd edition this was represented by them having a divine rank of 1 to 5. They could grant spells and do anything a god could do, just of a lesser power then other more powerful gods.

4th edition brought in the idea of extarchs and calls them demigods, but does not offer much explanation of what they are. But it does seem like extarchs are not true gods, but only divine servants or heroes. And by the 3rd edition divine ranking system that makes extarchs of a divine rank zero.

Or to put it simply: In 2nd/3rd edition demigod is a type of creature and a rank of power. In 4th edition demigod is just a title.