Green Leaders: From Past to Present

April 22 is Earth Day. Celebrated in more than 175 countries, Earth Day is a day for appreciating nature and raising awareness of how we can help preserve it. Environmentalism has lately become a popular cause in Hollywood where A-listers use their star power to advocate green living. But it's not just today's celebrities who have taken up the banner of environmentalism, famous Americans of the past helped bring nature into the public's consciousness. Here's a look at five famous conservationists:

Theodore Roosevelt

The 26th President of the United States had one of the most memorable personalities of any president. A macho figure with a fondness for the Wild West, Roosevelt fought with the Rough Riders in the Spanish American War. He wasn’t all tough, though. One of Roosevelt’s great passions was nature, and he was the first president to take up conservation as an issue of national importance. He was instrumental in preserving 230 million acres of land, including five national parks.

Ralph Waldo Emerson

Theodore Roosevelt was not the only famous American who had a historic love for nature. Ralph Waldo Emerson was one of the early American writers to focus much of his work on nature. In fact, his most famous essay, published in 1836, was titled Nature. Emerson advocated the notion that man is at his best when he is self-reliant and has a genuine relationship with the natural world. The publication of Nature led to the creation of Transcendentalism, one of the major American philosophical movements of the 19th century.

Brad Pitt

As actor Brad Pitt has reached new heights of fame, he’s become more and more involved with various causes. In addition to political issues, Pitt is an advocate of sustainable architecture. In 2006, Pitt founded the Make It Right Foundation, an organization that funded the building of houses in New Orleans’ Ninth Ward, a neighborhood that was largely destroyed by Hurricane Katrina. The Make It Right Foundation focuses on building with eco-friendly materials and affordable pricing.

Kristin Davis

Though she’s best known for being rich city girl Charlotte York in Sex and the City, in reaity Kristin Davis is a lover of the great outdoors. In 2009 she went on a trip to Africa to discover the wildlife there. While in Kenya, she discovered a lone baby elephant and had her transported to a wildlife rehabilitation center. Davis has been outspoken against poaching and the ivory trade, and in 2011 she was awarded the Humane Society’s Wyler Award for her efforts.

Leonardo DiCaprio

Among Hollywood stars today, Leonardo DiCaprio is one of the most well known for his environmental activism. DiCaprio drives electric and hybrid cars, has solar panels on his home and takes commercial flights in an effort to conserve energy. In November 2010, DiCaprio donated $1 million to the Wildlife Conservation Society.