Mammon is a false god used in the New Testament to describe material wealth or greed.
The word is assumed to derive from Late Latin 'mammon', from Greek 'μαμμωνάς', Syrian 'mámóna' (riches), Aramaic 'mamon' (riches), probably from Mishnaic Hebrew 'ממון (mmôn)'. (See refs: Winston 1954, Webster's 1977.) Other scholars derive Mammon from Phoenician mommon, benefit or Egyptian Amon-Ra (Amen-Ra, Egypt). Webster (1977) defines 'mammon' as: 1) the false god of riches and avarice. 2) riches regarded as an object of worship and greedy pursuit; wealth as an evil, more or less personified. Mammon is a term that was used to describe riches, avarice, and worldly gain in Biblical literature. It was personified as a false god in the New Testament. The term is often used to refer to excessive materialism or greed as a negative influence. Adjectival forms are mammonish and mammonistic per Winston 1954, Webster's 1977.
In his description, Mammon is somewhat similar to the Greek god Plutus, and the Roman Dis Pater, and it is likely that he was at some point based on them; especially since Plutus appears in The Divine Comedy as a wolf-like demon of wealth, wolves being associated with greed in the Middle Ages. Thomas Aquinas metaphorically described the sin of Avarice as 'Mammon being carried up from Hell by a wolf, coming to inflame the human heart with Greed'.
In the Bible, Mammon is personified in Luke 16:13, and Matthew 6:24, the latter verse repeating Luke 16:13. In some translations, Luke 16:9 and Luke 16:11 also personify mammon; but in others, it is translated as 'dishonest wealth' or equivalent. In some Spanish versions, it is said as "Mamón", but in others, as "Dinero" (Spanish for "money").
Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal: But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal: For where your treasure is, there will your heart be also.
No one can serve two masters, for either he will hate the one and love the other; or else he will be devoted to one and despise the other. You can't serve both God and Mammon. — Matthew 6:19-21,24
Early mentions of Mammon appear to stem from the personification in the Gospels, e.g. Didascalia, "Do solo Mammona cogitant, quorum Deus est sacculus"; and Saint Augustine, "Lucrum Punice Mammon dicitur" (Serm. on Mt., ii). Gregory of Nyssa also asserted that Mammon was another name for Beelzebub.
During the Middle Ages, Mammon was commonly personified as the demon of avarice, richness and injustice. Thus Peter Lombard (II, dist. 6) says, "Riches are called by the name of a devil, namely Mammon, for Mammon is the name of a devil, by which name riches are called according to the Syrian tongue." Piers Plowman also regards Mammon as a deity. Nicholas de Lyra (commenting on the passage in Luke) says: "Mammon est nomen daemonis" (Mammon is the name of a demon).
No trace, however, of any Syriac god of such a name exists, and the common literary identification of the name with a god of covetousness or avarice likely stems from Spenser's The Faerie Queene, where Mammon oversees a cave of worldly wealth. Milton's Paradise Lost describes a fallen angel who values earthly treasure over all other things.
Later occultist writings such as De Plancy's Dictionnaire Infernal describe Mammon as Hell's ambassador to England.
For Thomas Carlyle in Past and Present, the 'Gospel of Mammonism' became simply a metaphoric personification for the materialist spirit of the nineteenth century.