Sun Tzu (Chinese: ??; pinyin: Sun Zi; 544–496 BC) was the author of The Art of War, an immensely influential ancient Chinese book on military strategy. He is also one of the earliest realists in international relations theory.
The name Sun Tzu' ("Master Sun") is an honorific title bestowed upon Sun Wu (??; Sun Wu), the author's name. The word Wu, meaning "martial" or "military", is the same as the word in "wu shu" or "martial art". Sun Wu also has a courtesy name, Chang Qing (??; Cháng Qing).
Sun Tzu as a historical figure
The only surviving source on the life of Sun Tzu is the biography written in the 2nd century BC by the historian Sima Qian, who describes him as a general who lived in the state of Wu in the 6th century BC, and therefore a contemporary of one of the great Chinese thinkers of ancient times—Confucius. According to tradition, Sun Tzu was a member of the landless Chinese aristocracy, the shih, descendants of nobility who had lost their dukedoms during the consolidation of the Spring and Autumn Period. Unlike most shih, who were traveling academics, Sun Tzu worked as a mercenary. According to tradition, King Helu of Wu hired Sun Tzu as a general approximately 512 BC after finishing his military treatise, the bing-fa (The Art of War). After his hiring, the kingdom of Wu, previously considered a semi-barabaric state, went on to become the most powerful state of the period. Sun Tzu supposedly died when King Helu was killed in 496 BC.
Sun Tzu's own work is called in Chinese bing fa, which can be translated as "military methods," "army procedures," or "martial arts." Around 298 B.C., the historian Zhuang Zi, writing in the state of Zhoa, recorded that Sun Tzu’s theory had been incorporated into the martial arts techniques of both offense and defense and of both armed and unarmed combat. His "bing-fa" was the philosophical basis of what we now know as the Asian martial arts.
The historicity of Sun Tsu is discussed extensively in the introduction to Giles' 1910 translation available as a Project Gutenberg online text. In Lionel Giles' introduction to his 1910 translation of The Art of War, Giles expands on the doubt and confusion which has surrounded the historicity of Sun Tzu.
In 1972 a set of bamboo engraved texts were discovered in a grave near Linyi in Shandong . These have helped to confirm parts of the text which were already known and have also added new sections . This version has been dated to between 134-118 BC , and so rules out older theories that parts of the text had been written much later.
Sun Bin, also known as Sun the Mutilated, allegedly a crippled descendent of Sun Tzu, also wrote a text known as the Art of War. A more accurate title might be the Art of Warfare since this was more directly concerned with the practical matters of warfare, rather than military strategy.  At least one translator has used the title The Lost Art of War, referring to the long period of time during which Sun Bin's book was lost. There is, however, no commonality between the content or writing style in Sun Bin and Sun Tzu.
Sun Tzu also is rumored to be an ancestor of Sun Quan, the founder of the Wu Kingdom, which was one of the three competing super-dynasties during the Three Kingdoms era.
I have included The Art of War (without commentary) for the 'serious reader'.