The term "Renaissance Man" was born out of the trend back in the 14th-15th century for society to have a go at all sorts of interests: science, arts, literature, music, architecture, religion, history. This is a period renowned for the exquisite passion that was shown for all things equally, which is the reason why today we can enjoy the works of its major proponents: Michaelangelo, Da Vinci, Bramante, and the fascinating Italian and French projects.
Hence, by idiomatic definition, a "Renaissance Man" (or woman) is an individual who as a diversity of focal points which he or she wants to improve and excel.
Ben Franklin not only dwelved in the sciences with the creation of the house rods to detour lightning, the stove, bifocals, and the Poor Richard's almanac, but he was also a brilliant politician, a conversation maker, a charmer, an advocate, drawer, first class womanizer ;) and a historian of the first class.
Maybe you are, yourself, a Renaissance woman or man, if you have a tendency to diversify your interests and make them your own personal projects.
Franklin is considered by many to be a "Renaissance Man" because of his multiple talents. He represented so many things that it became difficult to categorize him. He was an inventor, as he is credited with many different inventions such as bifocals. He was a scientist, as the legends about his experimentation with electricity and the kite are well known. He was a political leader, as his role in the emerging nation has been highly documented. Additionally, he was a diplomat, charged with negotiating the peace with England and America and sent to France to do so. With both his Autobiography and "Poor Richard's Almanack," he was seen as a writer, also. Considered to also be self made and quite charming, Franklin is credited with being so skilled at so many thing that the term "Renaissance Man" becomes something used to describe him.
In addition to being a writer well known for his aphorisms and advice, Benjamin Franklin was also an accomplished prose writer. Some of his best known writings today are his Autobiography and his brilliant, short satirical pieces, including biting comments on British policies of shipping convicts to the New World as well as the New Englanders' biases against the Native Americans. See the two links below for samples of his satire.
Any good Renaissance man has to be good at letters or some other serious form of art, after all. (I'm not sure how serious a scientist he was, to be honest, but he certainly tried his hand at it, too.)
Benjamin Franklin is referred to as a "renaissance man" because he had a wide variety of interests and was quite learned in a variety of areas. The term "renaissance man" refers to a person like this -- one who knows something about everything, especially when it comes to things like science.
Franklin was, of course, a political and moral thinker. He published books of aphorisms and advice and was involved in the writing of the Constitution. But this was not all he did. He was also a scientist. He is well known for his experiment with the kite and the key during the lightning storm. He is also the inventor of the Franklin Stove.
So you can see that he was a renaissance man since he was able to think about politics on a high level but also be interested in (and good at) science and technology.