Aragorn in LOTR was a Dunedain Ranger. His costume in the movies is a cross between medieval and 1800's style dress. The secret to his costume is layers. First he has a grayish long-sleeved tunic. Over that he wears a long, brown leather sleeveless-type waistcoat. Over that he wears the long-sleeve 1800’s looking duster coat, and lastly he sometimes wears a cloak over all. You can buy leather coats and jackets from the thrift store, and cut these to be the sleeveless vest, or cut and put pieces together to make into the duster coat. Here are some sites to help you recreate this costume:

• A picture of Aragorn costume from The Two Towers Exhibit in Toronoto 2002
• Aragorn outfits by movie

Or you can just buy the costume version of this, though these may or may not be as comfortable to wear overnight on a hike:

• Aragorn costume at AnniesCostumes.com
• Aragorn clothing at the LRPStore
• Strider's Ranger Coat at MuseumReplicas.com