I second JZ's notion. Because of your stipulation for a blade at least 6" long, here's another vote for the Bark River Bravo 2 (7" blade). I have several "Barkies" and they are impressive. You're going to receive about as many suggestions as there are knifemakers.

If I had to pick just one of my knives, like Ken K I'd grab Doug Ritter's MK3. It's nicely balanced, substantial but not too heavy and I like the extended tang. An elegant tool. But the blade length falls short of your specs. And I'm not planning on fending off carnivores with it.

I'd bet that your brother would be delighted with the Bravo 2. It's beefy, but if you are thinking of stabbing a bear with it...beefy's good.

http://www.dlttrading.com/bark-river-knives-bravo-2.html

The Bravo 2 measures 12.25" overall with a 7" blade made of ultra durable A2 tool steel achieving hardness of 59HRC. Blade is a beefy .215" thick and the knife weighs approximately 14.5 oz. Comes complete with a deluxe Sharpshooter leather sheath.

$194-254, depending on the handle material you choose. DLT Trading has provided excellent service.

If I came to face-to-face with a mountain lion or brown bear armed with nothing but a knife I might drop dead of a heart attack.