Mjoll the Lioness

Mjoll the Lioness is a female NPC in The Elder Scrolls V: Skyrim. She has traveled the world extensively and claims to be as well traveled as one can be. However, in one of her most recent endeavors she was nearly killed by a Dwarven Centurion in the ruins she was exploring. It was only by the skin of her teeth that she was able to escape. Barely alive, she was saved by Aerin who then brought her back to Riften and nursed her back to health. While she recovered, he explained to her the corruption that plagued Riften. In order to honor Aerin and his aid in saving her life, she has sworn to do whatever she has to do in order to save the city. But it would seem she is having little success. The city has to want to save itself before she can save it.

Mjoll is a kindly, though intimidating, person. She gains the most pleasure from simply doing the right thing and earning people's trust than simply from a cash reward. She and Aerin can be found wandering the city, and in the Bee and Barb inn.

Interactions
When the Dragonborn first meets her in Riften, she talks about how she tires of the Thieves Guild and the other forms of corruption plaguing the city such as the Black-Briar family.

She will also give you a personal quest if you agree with her that The Thieves Guild in Riften is an evil (or, if you disagree with her, wait a few nights, then return to her), where you will be given the task to find and reclaim her sword named Grimsever, which she lost in Mzinchaleft (Dwemer Ruin). This ruin is the same one she was mortally wounded in before coming to Riften.

To receive Mjoll's quest you must be at least level 15 and have some level of positive standing in Riften. When first approached, she will tell you about the sword, but with no quest being activated. When you are of a sufficient level and standing, you can ask about the sword, starting the quest allowing you to retrieve the sword. If you go to Mzinchaleft before activating the quest, the sword may be replaced with a hide shield.

After successfully completing the quest, she can be asked to join you as a follower.

If for any reason at all, you harm Aerin, her 'savior' she will become moody and not want to talk with you as often. If you are married when you kill Aerin she will refuse to talk with you at all, claiming she is disappointed in you. If, however, you kill Aerin without the killing being observed, Mjoll will continue to interact with you as normal. A good way to do this is to wait until night and recruit Mjoll as a follower. Then order her to wait, follow Aerin back to his home, and murder him while sneaking.

Mjoll can be recruited for the Blades, but Aerin will follow her there. When engaging in a battle with a dragon alongside the blades, Aerin will follow and attempt to slay the dragon with his dagger. This usually results in his death.

Mjoll has been reported to kill NPCs over gear dropped on the ground, e.g. a belted tunic.

Marriage
The player can marry Mjoll if they possess and are wearing the Amulet of Mara. The player must also have completed her personal quest. She can be both a follower and a spouse simultaneously. When married, Mjoll opens a shop, and gives the player a profit of 100 Septims each day; everyday that you don't collect from her, it adds up.

Even when wedded with the player however, Aerin may sometimes continue following her. One solution to this particular bug is to kill Aerin.
 * The easiest way of killing Aerin when Mjoll is a companion, is telling Mjoll to wait inside a hold that is not Riften. Aerin will leave the hold and head back to Riften. He can be killed on the way back with no witnesses, and also without Mjoll hating you.
 * An alternative way to killing him. On PC, you can also use the console command "disable" while selecting him to make him disappear.
 * You cannot kill Mjoll after marrying her, so if you choose to marry her its permanent
 * She cannot be sacrificed at "Sacellum of Boethiah" in the "Boethiah´s Calling" quest. (Xbox)
 * The quest for Mjoll is short and worth it because she is a hardy and strong follower to have.
 * If you buy her armor (which is the banded iron armor set) she will walk around in her underwear after you leave your or her house.
 * If you marry Mjoll she will not equip any rings. My guess is when she gets the wedding ring it registers as worn even when you take it from her. (Xbox)
 * Even ifyou have done the quest and have the Amulet of Mara, it won't let you marry Mjoll. (Xbox) this can be fixed by speaking to Maramal, who is a priest with the temple of Mara, about marriage in Skyrim.