Marller

マーラー

Marller was once the childhood friend of the goddesses who serve as the main characters, although she is now a demon. Urd and Mara used to be very close friends, but they were separated when Urd chose to become a goddess.
Although Mara is the arch-rival of the goddesses, she enjoys their company. Her actual duty is to increase the market share of demons on Earth; her primary responsibility should be signing demonic contracts with humans, while her secondary duties include ruining the goddesses' activities, disrupting their efforts, and causing them to suffer. However, she typically neglects her main duty and focuses only on the secondary ones, having decided at the start of her appearance that the market share would reach 100% once the goddesses were eliminated from this segment of the market.
Mara has two weaknesses: she cannot stand good luck charms, and she cannot stop dancing when she hears rock music (or disco, in the Dark Horse English translation).
Marller appears more determined and mischievous than outright cruel. She felt abandoned when Urd chose to fully become a goddess, knowing this would likely end their friendship. This past experience, combined with her duties as a demon, gives her a slight case of tunnel vision, making her regard ruining the lives of the goddesses as a top priority. Despite this, she seems to enjoy the company of the goddesses whenever the opportunity to hang out with them arises.
In the TV series, Marller is revealed to suffer from insecurity and self-doubt due to her inability to increase the demons' market share (largely because of the goddesses' presence), to the point of bringing her to tears when Urd tells her that she has no talent.
You may see Mara referred to by several other names, such as Marller or Marla. Marller is how Mr. Fujishima romanizes her name when it is written in Roman characters, and Marla is how it sounds when pronounced by a Japanese speaker, as well as the romanization used by Geneon Animation for the Mini-Goddess series. In Buddhism, Mara is also the name of a demon who tempted Gautama Buddha by trying to seduce him with the vision of beautiful women. Similarly, in the series, Mara uses such tactics on Keiichi in her first appearance by using Sayoko to distract him from Belldandy. The reason most Japanese speakers prefer not to pronounce her name as Mara is that the word 陰茎, romanized as "mara", is Japanese for "penis".