Mad Moxxi (voiced by Brina Palencia) is first introduced in the Borderlands DLC episode Mad Moxxi's Underdome Riot as the owner and host of Pandora's biggest fighting arena, the Underdome. Having been a skilled fighter in her earlier years, Moxxi loves violence and combat, and she especially loves being at the center of it all.
Her sense of modesty definitely isn't what Moxxi is known for, though, as she has had several husbands, lovers both male and female, and innumerable affairs. Despite this, Moxxi is surprisingly refined in her tastes and mannerisms, always speaking with a seductive tone and an innuendo soon following. She can also be quite caring and sympathetic, especially in regards to her children and others close to her.
She appears again in the third DLC episode The Secret Armory of General Knoxx, running a bar called Moxxi's Red Light where Athena takes refuge in and instructs the Vault Hunters to meet her at. By the time the Vault Hunters arrive, however, Athena has already been taken hostage by Moxxi's second ex-husband Mr. Shank. Moxxi reveals what happened and helps the Vault Hunters locate and rescue Athena in Lockdown Palace. When Shank is killed in the process, however, she is stricken with grief over the death of her ex-husband and tearfully begins making funeral plans as the Vault Hunters are making their way out of the prison.
In Borderlands 2, more of Moxxi's life and family is revealed. Moxxi and her children (including Scooter and Ellie) originally grew up in the hillbilly Hodunk Clan out in the desert but left when she refused to let Ellie become the clan-wife. She is ashamed at her Hodunk origins and hides her thick redneck accent beneath her seductive voice, though she occasionally slips if tipped heavily enough in her bar, after which she begs the Vault Hunters to not tell anybody. Moxxi was also involved with Mordecai for a time after the first game until she dumped him for Handsome Jack, though she dumped Jack when she saw just how much of a despot he really was. Jack burned down Moxxi's Underdome shortly afterwards, leaving her bitter and itching for revenge as she relocated to Sanctuary and became the owner of the local bar. She gets her revenge when she hires the Vault Hunters to kill Jack's foreman in Opportunity and flood the building site, which causes Jack to angrily call Moxxi a "bitch".
During the DLC Mr. Torgue's Campaign of Carnage, which takes place during the events of Borderlands 2, Moxxi acts as the Vault Hunters' sponsor in an effort to claim Mr. Torgue's arena and rebuild the Underdome. She first appears as the hostage of arena contender Pyro Pete, although it is unknown how she ended in his custody. Once rescued, she helps the Vault Hunters hunt down her cannibalistic ex-girlfriend Motor Momma. She also attempts to talk the Vault Hunters out of murdering a man whom she had sexual affairs with and whom Scooter had ordered the Vault Hunters to eliminate, although whether or not the murder is carried out is up to the discretion of the player.
She later appears as the host of the penultimate DLC Mad Moxxi and the Wedding Day Massacre, where she attempts to end the feud between the Hodunks and their Irish-inspired rivals, the Zafords, by having the Vault Hunters concoct a potion that will make a pair of goliaths, one from each clan, fall in love. The potion works, but the goliaths enter their berserk state soon after and are killed by the Vault Hunters in the ensuing battle. The Hodunks and Zafords then band together and declare war against Moxxi.
In Borderlands: The Pre-Sequel, Moxxi has set up a bar in Elpis's port town of Concordia and works with Jack and his Vault Hunters to prevent Zarpedon from destroying Elpis with the Eye of Helios. However, Moxxi's actual goal is to sabotage the Eye of Helios so that Jack does not turn it against Pandora out of his hunger for power. She is revealed to be just as good a mechanic (if not better) than Scooter or Ellie and that she relapses into her Hodunk personality when she's working, but Moxxi warns Jack's Vault Hunters not to tell anybody or she'll have Scooter bury them in shallow graves (echoing how he killed Lucky Zaford).
In Zoomin.TV Games' "Top 5 MILFs in Gaming" video, Mad Moxxi was awarded first place, calling the character "mad as a box of squirrels and equally as alluring, Mad Moxxi is unquestionably gaming's number one MILF," also showing players how to get under the Borderlands 2 map to get an upskirt view of Moxxi in the bar.