Short answers, pulled from the story.
Tolkien explicitly named Samwise Gamgee the "chief hero" in his own writings, arguing that Sam's loyalty and his love for Rosie Cotton were "absolutely essential" to the story's meaning. He valued heroism rooted in devotion rather than in power or ambition. Sam's willingness to return the Ring when he briefly held it was, in Tolkien's reading, the defining proof of that devotion.
The surname "Gamgee" comes from a colloquial Birmingham word for cotton wool, itself derived from Gamgee Tissue, a surgical dressing invented by the 19th-century surgeon Sampson Gamgee. The forename translates the Old English Samwís, meaning "halfwise" or "simple." Tolkien developed the full modern form through a series of stages from Sam's Westron name Banazîr Galbasi.
In March 1956, Tolkien received a letter from a real man named Sam Gamgee, who had heard his name was in The Lord of the Rings but had not read the book. Tolkien replied politely and sent him a signed copy of all three volumes. He later recorded in his journal that he then lived in fear of a follow-up letter signed "S. Gollum."
Sean Astin played Samwise Gamgee in all three of Peter Jackson's films: The Fellowship of the Ring in 2001, The Two Towers in 2002, and The Return of the King in 2003. Earlier screen portrayals include Michael Scholes in Ralph Bakshi's 1978 animated version and Roddy McDowall in the 1980 animated television version of The Return of the King.
Samwise Gamgee was elected Mayor of the Shire seven consecutive times, with his first election in the year 1427 of the Shire Reckoning. Each mayoral term lasted seven years. His descendants later adopted the surname Gardner in his honour.
Tolkien wrote in a private letter that Sam was "a reflexion of the English soldier, of the privates and batmen I knew in the 1914 war." A batman was a personal military servant assigned to an officer in the British Army, and Tolkien himself served as an officer. His biographer John Garth described the relationship between Sam and Frodo as mapping closely onto the social gulf and hierarchy of a British Army officer and his servant.