Cthugha
Cthugha was an addition to the Cthulhu Mythos in the 1940s, during the decade just after the death of Howard Phillips Lovecraft. Cthugha is a controversial addition to the body of Lovecraftian works, because he's representative of a number of concepts that many Cthulhu fans and historians feel have been grafted onto the stories by others. That's certainly the case, though the issue at dispute is whether an author like H.P. Lovecraft, who valued his literary friends and encouraged their contributions as much as he did, would so much mind his friends and fellow writers taking liberties with his creations. In either case, Cthugha represent a powerful force in the universe created by Lovecraft--unless you're a purist who doesn't take August Derleth's writings as canon.
The House on Curwen Street
Cthugha came into the world of Lovecraft when August Derleth wrote "The House on Curwen Street" in 1944. Thus, Cthugha was one of many addition to the Cthulhu Mythos that appeared after the death of H.P. Lovecraft in 1937. Cthugha is a strange fit into the mythos pantheon, since he's a Great Old One opposed to most of the other Outer Gods.
August Derleth's Cthulhu Mythos
August Derleth was early-on responsible for collecting and organizing Lovecraftian tales. When other publishers would not print the remaining collected works of Howard Phillips Lovecraft, August Derleth and Donald Wandrei founded Arkham House publishing and published the stories themselves. Arkham House became an important publisher of horror content and still remains in existence to this day (controlled most of that time by Derleth's children and grandchildren). No one disputes August Derleth's contribution to H.P. Lovecraft's legacy and many famous Cthulhu Mythos authors like Brian Lumley and Ramsey Campbell have acknowledged August Derleth's guidance in their early careers.
That hasn't stopped many commenters and fans of the Cthulhu Mythos from criticizing August Derleth. Even the name "Cthulhu Mythos" was created by August Derleth--and some have noted that Lovecraft called the tales Yog-Sothery (not a better name, in my opinion). S.T. Joshi and others were critical of the period when August Derleth would write Cthulhu stories from scraps of information H.P. Lovecraft left behind. These short stories were often attributed to H.P. Lovecraft and August Derleth together, so that critics have claimed Derleth appropriated Lovecraft's name posthumously to get his fiction published. This somewhat overlooks the fact that Lovecraft's name wasn't a huge lure to publishers at the time (in the years proceeding his death) and that August Derleth was an established writer at the time--Derleth considered his voluminous writing outside the horror genre to be his key contributions to literature.
Perhaps a more important criticism is that August Derleth introduced his own Christian worldview of good-versus-evil into the Cthulhu Mythos. H.P. Lovecraft's universe was an amoral one in which the human race was beneath the notice of the Elder Gods. Lovecraftian horror owed a lot to the works of earlier writers like Lord Dunsany, but it also captured the zeitgeist of the 1920s. In a decade when Albert Einstein had proven that common sense was wrong and the universe was a whole lot stranger and more cosmic than we ever conceived before, a writer created cosmic gods that warped reality around them or represented strange geometry was a far cry from the Christianity of August Derleth. So to pit creatures of basic goodness like Cthughu against the Cthulhu pantheon radically alters the entire fictional universe.
Cthugha and Elemental Fire
Another difference with Cthugha (and other Derleth creations) is his connection to the classical elements. Since the time of the ancient Greeks, the four base elements (fire, water, earth, air) and sometimes a fifth element (quintessence or ether) had cropped up in occult lore. The early Lovecraft short stories have no trace of such "mundane" concepts and, in fact, represent strange forces that are set against or paradoxical to the world most humans know and perceive. Beings like Yog-Sothoth and Azathoth might represent fundamental forces, but they represent mind-bending concepts that drive a man mad to understand. Thus, having a being that represents an element as basic as fire (like Cthugha does) is out of line with what came before.
Cthugha's Appearance
That being said, the tale of Cthugha still bring a sense of cosmic scale and wonderment to them. As originally described, Cthugha exists as a giant ball of fire. Sometimes, you'll see Cthugha depicted as looking a bit like Cthulhu, but having a fiery form. In games like Arkham Horror, you'll see Cthugha depicted as an elemental force and opponent to mankind, though in stories by August Derleth such as 1944's "The Dweller in Darkness", you'll see the protagonists trying to summon forth Cthugha in order to drive away Nyarlathotep.
Cthugha Fire Vampires - Cthugha Fomalhaut
The alien worshippers of Cthuga are known as the fire vampires. There are two types of them: the "flame creature of Cthugha" created by August Derleth and the "fire vampires of Fthaggua" created by Donald Wandrei. They are described as points of light that follow Cthugha everywhere he goes and set on fire anything flammable they touch. The creature Fthaggua is certainly a priest of Cthuga, but he may also be a spawn of that creature, as well. Some dispute surrounds that question. It's thought that Cthugha and the star known as Fomalhaut are connected.
Cthugha Ogre
Cthugha was appropriated as a name by the Ogre software people for the name of their latest download. The Ogre people are known to name their products things like "Azathoth", so it was just a matter of time. If you see terms like "Cthugha Ubuntu", "Cthugha Source", "Cthugha Linux", "Cthugha Download", Cthuga-l, or "Cthugha Winamp", just ignore those search results and continue to research H.P. Lovecraft. For those who found this page with any of those terms, I hope you enjoyed reading about why Ogre names their products weird names like "Cthugha".