"Still the iron claw in the velvet glove, Mariel?"
- – Timov, 2259
Mariel was one of Londo Mollari's four wives.
Courtships and Intrigue
Before her marriage to Londo, a very young Mariel had been courted by two promising noblemen in the military; Solla and Riva. Solla was the more promising and at her father's instruction Mariel willingly accepted his advances, much to Riva's consternation. Not willing to let the matter drop Riva attempted to fight Solla for Mariel's hand though was soundly beaten. After which Riva publicly swore vengeance against his rival suitor and when Solla and his younger brother Durla both fell ill from poisoning, suspicion instantly fell on Riva. Though Durla survived, Solla eventually succumbed and when the other members of their squad moved to arrest him, he very stupidly made the terminal error of resisting arrest.
With both of Mariel's suitors dead, the late Solla's younger brother Durla approached Mariel and confessed his love for her. Mariel had only been interested in Solla and Riva because they had potential and were destined for greater things had no interest in Solla's lesser brother, the "pathetic" Durla and cruelly dismissed the young man. Unknown to all at the time it had actually been Durla who had poisoned both his brother and himself and allowed the blame to fall of Riva.
Shortly thereafter, Mariel had become linked with House Mollari and her father arranged for her to wed the much older nobleman, Londo Mollari. Unnoticed by either newly wed, Durla had attended the bonding ceremony.
Married to Mollari
Mariel was the youngest of Londo's three wives by many years. Soft spoken and beautiful, she lavished affection on Londo, but did not truly love him. She maintained numerous affairs, as Londo explained she was attracted to men of power like a moth to the flame--but she burned them.
In 2259, Emperor Turhan offered to grant Londo any one wish that he desired. He requested a divorce from the arranged marriages to his three wives: Mariel, Timov, and Daggair. One condition was presented which was to keep at least one of the wives. He invited all three of them to come to Babylon 5 so he could deliver the news personally, just before having an anniversary party for his Day of Ascension. Mariel knew what was going on and, not willing to chance him choosing someone else, arranged with an old associate of hers, Matthew Stoner, to have a Centauri artifact brought to Babylon 5, a statuette that had been booby-trapped by the Narns to fire a poison dart when triggered by the touch of a Centauri. Stoner gave the artifact to a trader in the Zocalo, telling him that an elegant Centauri woman would come by and indicate that she wanted to purchase it by pointing at it.
Whereas Timov made no pretenses regarding her feelings toward Londo, Mariel put on a display of affection for him after arriving on the station, seemingly endeavoring to be the one kept. She gave the artifact to her husband at the party. The trap poisoned him, bringing him close to death. Mariel pouted and protested her innocence, though the other wives paid no attention to her.
However, Londo does recover. While he recuperates in Medlab, Mariel visits one of her lovers--none other than Londo's hated rival, G'Kar of the Narn Regime. G'Kar explains that he knows full well she not only knew the device was trapped but identified herself as the giver to throw suspicion elsewhere. He warns her Londo is likely to figure it out as well, though Mariel does not seem concerned.
Ultimately, Londo chose to keep Timov because he always knew where he stood with her. He did offer Mariel a modest alimony as a settlement, but she would no longer be able to live the privileged life of a noble she was accustomed to. 
As a discard, Mariel found herself something of a pariah in Centauri social circles, a situation that only worsened after her ex-husband became the emperor. Living alone in her family estate and running out of funds, she was composing a suicide note when she was visited by Throk Milifa and brought to Chancellor Castig Lione. Based on the recomemndation of Durla, who was now Minister of Internal Security, Lione offered Mariel a job in the Centauri Republic's new espionage division, which was codenamed the Division of Public Works. Mariel accepted, and recommended certain other individuals of her acquaintance whom she felt would prove useful to the new division.
As an agent of the Division of Public Works, Mariel traveled to Babylon 5 and set up base there, seducing Centauri Ambassador Vir Cotto and using him to get herself in contact with various ambassadors and officials of the Interstellar Alliance. Mariel had little trouble in charming the male diplomats and officials, using her charisma to her advantage even with species who would not find a Centauri physically attractive. She spent the next several months going between Babylon 5 and assorted planets. Her duplicity was eventually revealed to Vir by a young techno-mage named Kane.
Seeking revenge on Mariel for making a fool of him, Vir had the techno-mage Galen cast a love spell on her, making her utterly devoted to Ambassador Cotto. Vir then used her to get himself into the good graces of Durla and his cronies, the dominant faction of the Centauri royal court, and purposefully lost her to Durla in a game of poker. Mariel became Vir's spy in Durla's midst. In 2271 Mariel and Durla were married around the same time that the latter was elected Prime Minister.
- According to ("Soul Mates") writter Peter David; Mariel corresponds to "Death."
- During the scene in Londo's "Day of Ascension" party wherein G'Kar is being accosted by Daggair for wearing shoes (a grave insult, it seems), G'Kar is seen throwing a small grape at Mariel, secretly. The passing of fruit is a part of Narn courtship rituals and symbolizes sexuality.