Nergal is the (southern) Mesopotamian god of death, pestilence and plague, and Lord of the Underworld.
Nergal represents a very particular aspect of death, one that is often and rightly interpreted as inflicted death, for Nergal is also the god of plague and pestilence as well as being closely associated with warfare. Nergal's warlike qualities identify him to a considerable extent with warrior gods such as Ninurta and Zababa (Van der Toorn et al. 1999: 622). In his aspect of a war god, Nergal accompanies the king into battle, delivering death to the enemy. Death brought on by Nergal also had a supernatural dimension, disease often being attributed to demonic agency in Mesopotamia. Indeed, Nergal controls a variety of demons and evil forces, most notoriously the ilū sebettu, the "Seven Gods" who are particularly prominent in the myth of Erra as agents of death and destruction (Foster 2005: 880-911). Nergal's association with demons and disease further enhances the apotropaic qualities attributed to him and his circle, although such qualities are often attributed to chthonic deities as a class. The Late Babylonian apotropaic figrines representing Nergal (Ellis 1968) or the use of the Erra epic as house amulets (Reiner 1960b) can be seen as a manifestation of this.
Nergal's earliest incarnation is in the Early Dynastic Period as Meslamtaea, the god of the underworld whose main cult centre was in the city of Kutha (Lambert 1973: 356). From the Old Babylonian Period onwards, Nergal was syncretised with Erra, a Semitic death god (Wiggermann 1998-2001d: 217). Son of Enlil and Ninlil or Belet-ili (Black and Green 1998: 136), Nergal had several spouses: Laṣ, a little-known goddess of possibly non-Sumerian origin; Mamma/Mammi/Mammitum (Lambert 1973: 356), likewise a relatively minor deity; Ninšubur, attendant of Inana/Ištar; Admu, a West Semitic goddess (Wiggermann 1998-2001d: 219-20); and finally Ereškigal, to whom his marriage is a relatively late development. In the myth of Nergal and Ereškigal (Foster 2005: 506-24), Ereškigal reigns as queen of the underworld into which Nergal is sent to apologize for having offended Namtar,Ereškigal's vizier. There, Nergal is seduced by Ereškigal but manages to trick his way out of the netherworld, otherwise known as "the land of no return". Ereškigal is beside herself with grief at the loss of her lover and finally has him brought back to her. From this point onwards, they rule the underworld jointly (Gurney 1960). Nergal seems to have been 'forced' into this union in more ways than one, for the myth probably reflects a deliberate attempt in the Old Babylonian Period to reconcile northern and southern Mesopotamian traditions which ascribed rule of the netherworld to Ereškigal and Nergal respectively (Dalley 2000: 164).
Kutha was the main cult centre of Nergal (Wiggermann 1998-2001d: 217), who also enjoyed patronage over Maškan-Šapir (Stone and Zimansky 2004). Cults of Nergal are also attested for Dilbat, Isin, Larsa, Nippur, Ur and Uruk (Van der Toorn et al. 1999: 622).
Earliest evidence on Nergal is as the Kuthean god Meslamtaea, in god-lists from Fara and Abu-Salabikh (Lambert 1973). The name Nergal first appears in the Ur III period (Wiggermann 1998-2001d: 217). In the second millennium, Nergal comes to co-rule the underworld with Ereškigal. In the Neo-Assyrian period, he is attested as a significant figure in official Assyrian cult (Van der Toorn et al. 1999: 622).
Nergal is often portrayed as an astride male figure carrying a scimitar or a mace, the mace often being topped by a (double) lion's head. He is also associated with the bull (Wiggermann 1998-2001e: 223-4).
Yaǧmur Heffron, 'Nergal (god)', Ancient Mesopotamian Gods and Goddesses, Oracc and the UK Higher Education Academy, 2016 [http://oracc.museum.upenn.edu/amgg/listofdeities/nergal/]