They can absorb more punishment than you (technically, since they're difficult to kill) and at early levels, they might be stronger than you.

Hypercompetent Sidekick: They can generally scout traps and be aware of an enemy's presence before you are.

They won't hesitate to murder a defenseless old lady if you give them the order.

Bodyguarding a Badass: That badass being you, of course.

Bodyguard Crush: If you wear an Amulet of Mara while speaking to them.

Blonde, Brunette, Redhead: Jordis, Lydia, and Iona respectively.

Starting with Hearthfire, they share this position with your Stewards.

Battle Butler: They carry your goods if you request it, and, when not following and protecting you, they stay at home to guard your house, your children and anything you own.

But they won't hesitate to use a staff if you give one to them, or it is lying around for them to use.

Badass Normal: They don't need fancy magic or an ancient language to keep up with the Dovahkiin.

Artificial Brilliance: If a fight is beginning to look a little one-sided, they'll snatch up a staff they found lying on the ground and use it to even the odds.

They will do everything in their power to protect the Dragonborn's children from bandits and other random attacks.

Action-Hero Babysitter: With the addition of the Hearthfire DLC, the housecarls become these.

With Hearthfire installed, you can also gain housecarls from Falkreath, Hjaalmarch, and the Pale's Jarls after purchasing land (Winterhold alone does not have purchasable property). In order to earn a housecarl, you must become a Thane (in other words, an acknowledged hero of the hold), which generally involves directly assisting the Jarl in question, helping the citizenry of the hold, and, in the case of the major holds (Whiterun, Eastmarch, the Rift, the Reach, and Haafingar), purchasing property. Housecarls are warriors assigned by the Jarl of a hold to protect the Dragonborn and their property.

List of all followers in skyrim