If someone wants his job to take place mostly in the wild, what kind of career should he look into?
This depends on a great number of personal preferences.
Adventure Company Guide - If you want to lead others in a purely recreational sense, you can be a guide for one of the many adventure companies. Some examples of these companies are here: http://adventure.nationalgeographic.com/adventure/outfitterhome
Outward Bound and NOLS - If you want to lead others in the outdoors with some element of education or development, the biggest names in the United States are probably Outward Bound (outwardbound.net is their international site) and NOLS (nols.edu), which run very good, very well reputed programs. They also run international programs.
Wilderness Therapy - If you want to help people therapeutically in the outdoors (counseling, guiding, etc.), you could work for a company that does what is called "wilderness therapy." Examples would be Open Sky Wilderness Therapy (openskywilderness.com) or Anasazi Foundation (anasazi.org).
National Parks Interpreter - If you want to educate others in the outdoors, there are lots of interpretive programs through the National Parks, as well as many schools that are primarily outdoor or experiential oriented. (Examples: http://www.christodora.org/ http://www.hooksumschool.com/)
Outdoor Athlete - If you want to be a professional outdoor athlete, you could become very good at skiing/snowboarding/climbing/etc and get work that way. Along the same lines, you could be involved in video production companies that work on climbing or ski films (such as Sender Films or Big Up Productions).
Field Scientist - If you're interested in the sciences, you could be a botanist, biologist, forester, or natural resource specialist. The National Park Service & other federal land management agencies often hire lots of these types of people, and they get to hang out in the outdoors all day.
University - If you want to help others experience the outdoors you could work for a college or university outdoor program. Some of them offer very interesting programs and trips, and even degrees such as Adventure Education (www.fortlewis.edu, www.prescott.edu), Experiential Education, or Recreation Management.
Archaeologist - especially one who works in Cultural Resource Management (CRM) (often includes private companies that survey for oil pipeline projects or power lines, etc)
I'm sure there are lots of other options I haven't listed, too. Looking at the types of jobs you might be into, there are several websites to peruse: www.outdoored.com (they have articles and a job search function) www.aee.org (Association for Experiential Education - they have lots of jobs and articles in the realm of experiential education) www.bluefishjobs.com (lots of jobs that have an outdoor element - sometimes you have to search hard to find fun ones)
Good luck. Hope this helps.
A good outdoor job that allows for much hiking and outdoor activity is that of an archaeologist, especially one who works in Cultural Resource Management (CRM) (often includes private companies that survey for oil pipeline projects or power lines, etc), or for one of the federal land/wildlife management agencies, such as the National Park Service (NPS), the Bureau of Land Management (BLM), the US Fish & Wildlife Service, or the US Forest Service (USFS).