Yes. One of the leaders Roosevelt looked to was George Bird Grinnell. Grinnell was a friend of the Audobon family from New York. He graduated from Yale and became the first political activist in the conservation era that we all trace our hunter-conservationist roots to. He used his role as the editor of Forest and Stream Magazine (Now Field and Stream) to take some serious shots at the politicians who were working to destroy what he had come to admire during his time in the west. In addition to wildlife and the landscape, he was amazingly well-schooled in native culture, later becoming an activist on behalf of native people.
The best book I have found that best explains Grinnell's influence and how Grinnell bridged the gap from Audubon to Roosevelt is Michael Punke's - Last Stand: George Bird Grinnell, the Battle to Save the Buffalo, and the Birth of the New West.
Grinnell eventually formed the Audubon Society that we know today. If not for Grinnell, wildlife in Yellowstone Park would have been poached by market shooters. The bison of the plains would have completely perished. The start of modern day game laws and protections, such as the Lacey Act, were advocated for and made reality by Grinnell. As one of the founders of the Boone & Crockett Club, along with Roosevelt and others, Grinnell used the influence of that group to make a huge difference in wildlife and conservation.
Some might go further back than Grinnell, maybe to Audubon, or George Perkins Marsh. Both had a big influence on Grinnell. The country had not yet depleted its seemingly inexhaustible resources during the time of Audubon and Marsh, but by the time Grinnell grew to his positions, it has become apparent that there were limits to the land and the wildlife. Grinnell took their teachings and writings and put them into a new idea called conservation. Once Roosevelt joined in, he used his political influences to make some huge strides against odds that make today's challenges seem rather pedestrian.
Long answer, but that is where I would start. From Grinnell, the family tree of conservation goes many directions. You can spend the rest of your life reading the many books of how we got to where we are today. And in doing so, you will realize that as much as things change, when it comes to politics and our societal views and wildlife/wildlands/conservation, history has a tendency to repeat itself. Today could be no better example.
If you want some other stuff of people who influenced Grinnell when serving as his hunting guide, James Willard Schultz writes some of the best stuff out there, as far as adventure hunting in the mid 1870'-1880's. I have read his book My Life as an Indian many times. As I have his book Blackfeet and Buffalo, preferring the former a bit more of the two.
If hunting with Schultz was anything like reading his books, Grinnell must have had the time of his life while on those hunts. I think there was good reason why Grinnell gave Schultz as much magazine space as Schultz could supply him with.
