Stenvar is one of my favorite followers in Skyrim. This mod makes the following changes that (in my opinion) make him even better:

1) Stenvar has a new, younger look; he's still a big bearded dude but he's not quite so haggard anymore.
2) Stenvar's default outfit is now clothing instead of steel armor, meaning he will wear any armor you give him (note that in the screenshots, he's wearing iron).
3) Stenvar is now essential.
4) Stenvar will level with you from 10 all the way up to 81.
4) Stenvar will now use whatever bows you give him--- you can remove and sell his default hunting bow (this actually applies to all followers).

To install, just download the file and copy the .esp and the Textures folder into Skyrim's Data folder. When you run Skyrim next, check "stenvar.esp" in the list and then play.

Stenvar may have a neck seam when you first meet him. If so, you can fix it by selecting him in the console and entering the following console commands:
setnpcweight 100
disable
enable

Stenvar's face can also be downloaded as a playable male preset here: http://skyrim.nexusmods.com/downloads/file.php?id=15641 .

If this mod changes Stenvar too much for you, check out greyblood's AMAZING and more subtle "Stenvar - Colossal Crusher" mod at http://nexusmods.com/skyrim/mods/24659 .

In the screenshots, he's wearing the Blades Armor redesigned in HD by Inosite and the Gattis Belt Collar by Originally Gattis modified by SourAndSweet.

I am prone to missing details and making stupid errors so leave me a comment if you notice any issues.