Quoth Wikipedia, emphasis mine:
The utukku were a type of spirit in Sumerian religion that had escaped the underworld, either by their own power or by being summoned forth by a priest, such as the one appearing in the Epic of Gilgamesh. They could be either benevolent or evil. The evil utukku were called Edimmu and the good lamassu or shedu. Two of the best known edimmu were Asag (slain by Ninurta) and Alû. Though they are sometimes confused for The Seven Evil Spirits, an utukku is the raised spirit of a mortal, while The Seven were created by Anu as plague gods.
The only other source I have consulted does not make mention of Asag as the spirit of a deceased mortal, instead, he is said to be a creation of An, the city-god of Uruk. I cannot remember having ever read anywhere of his origin being anything else.
I've been trying to research whether careless editing by different authors has perhaps created this problem by leading to a failure to classify Asag as one of those "Seven Evil Spirits" mentioned in the passage as not being the spirits of the dead, but this endeavour has been thwarted by the inclination of the term being used in conspiracy theories, to the point where I am unable to find any sources appearing reasonable foundations for the assumption that such "Seven Evil Spirits" existed at all, not to speak of ascertaining their names and attributes with any clarity.
As for the Shedu, I have no particular sources at hand, but remember to always have learned of them as minor protective deities in a messenger function from the larger divinities of the pantheon and perhaps also their creation - that is, directly, and not via an interposed mortal existence, death and subsequent escape from the underworld, followed by entering the employ of the gods.
Could someone elucidate the bed of this mythological mire?
Asag is referred to as the offspring of An (the sky) and Ki (the earth). In a song (Sumerian šir) to Ninurta, the speaker explains the origins of Asag.
Heaven copulated with the verdant Earth, Ninurta: she has born him a warrior who knows no fear -- the Asag, a child who sucked the power of milk without ever staying with a wet-nurse, a foster-child, O my master -- knowing no father, a murderer from the mountains, a youth who has come forth...
The monstrous Asag quickly assumed dominion over the mountains and stones.
The plants have unanimously named it king over them; like a great wild bull, it tosses its horns amongst them. The šu, the saĝkal, the esi (diorite), the usium, the kagena (haematite), and the heroic nu stones, its warriors, constantly come raiding the cities. For them a shark's tooth has grown up in the mountains; it has stripped the trees. Before its might the gods of those cities bow towards it. My master, this same creature has erected a throne dais: it is not lying idle. Ninurta, lord, it actually decides the Land's lawsuits, just as you do. Who can compass the Asag's dread glory? Who can counteract the severity of its frown? People are terrified, fear makes the flesh creep; their eyes are fixed upon it. My master, the mountains have taken their offerings to it.
Mesopotamia had several different protective and tutelary deities, including the female lama (Akkadian lamassu) and the male alad (Akkadian šēdu). These were usually shown in humanoid form and were most commonly seen on seals and seal impressions, where they presented the seal-owner to a god. Here you can see an example from the Ur III period. These protective spirits are to be distinguished from the ghosts of the dead (Akkadian eṭemmu), which were usually malevolent.
In a literary example from the Tale of the Righteous Sufferer (Ludlul bēl nēmeqi), the sufferer bemoans that his protective spirits have abandoned him.
islit šēdu dumqi ša idīya iprud lamassīma šanâmma išē
The favorable šedu of my side split away; my lamassu was afraid and found someone else.
A different, hybrid protective spirit became particularly popular during the Neo-Assyrian period. This spirit, known as an aladlammû, took the form of a bull/lion with a human head and (often) wings. There is a very fine example in the Oriental Institute of Chicago; the British Museum and the Louvre also contain examples.
The aladlammû are best known textually from the quarry scene of Sennacherib. The accompanying text describes the action.
I had men from enemy towns and the inhabitants of hidden mountain regions, the conquest of my hands, wield iron qulmû and akkullu tools, and I had great aladlammû figures made for the gates of my palace.
