Its an alligator gar, and I believe that one was shot/caught on Sam Rayburn Reservoir in SE Texas. They're pretty common in the eastern third of Texas, and the rest of the humid parts of the western gulf coast. That one is definitely bigger than normal, but 'gator gar over 5' and 100 lbs are pretty common.

As far as what kind of fly gear it would take to land it, its probably near impossible on one that size. Not only do the look sorta like an alligator, they kill their prey the same way- the "death roll". Whether killing prey or reacting to a hook, a 'gator gar will start rolling violently. A barracuda type leader would be necessary to have a chance to catch one, but if the fish rolls and get all of the leader and part of the flyline wrapped around it, 8" of steel wire doesn't help much.

On the possibility of eating them, that's rarely done. (by folks with over 10 teeth, anyway) A gar that size is likely over a hundred years old, and antique meat don't taste too good. The roe of alligator gar are also quite poisonous to humans, so great care must be taken when cleaning the fish to keep any of the eggs juices from tainting the rest of the meat.