Ralph Sawyer, in his introduction to his translation of The Art of War, concluded with this in the section on Sun-zi's (as it would be written using today's pinyin system) life:

Sun Wu (ed: that's Sun-zi's suspected historical name - the "tzu/zi" you see at the end of most Chinese scholars' names is similar to an honourific) remains an enigma not only because of the absence of historical data in the so-called authentic texts of the period, but also because his life never generated the anecdotes and illustrative stories frequently found about famous figures in the works of succeeding periods...Many theories have been vociferously advanced to explain Sun Wu's invisibility, chief among them that most of the credit that was rightly his was attributed to his mentor, Wu Tzu-hsü, because the latter was more prominent and his life, a living melodrama writ large, provided a natural focal point for tales of intrigue and portraits of achievement. (Sawyer 1994, 84)

Sawyer quotes two primary sources to demonstrate the inconclusiveness of what we know about Sun-zi: the Spring and Autumn Annals of Wu and Yüeh and the Shih chi, the latter being "China's first true history and a literary masterpiece" containing the biographies of military strategists and generals. These two works disagree as to Sun-zi's origins and military achievements. As well, Sawyer notes that some historians dispute Sun-wu's (the historical person believed to be the author, not necessarily the actual author since clearly someone wrote Art of War) actual existance because he was not mentioned in the Tso chuan, "the classic record of the period's [ed: the Spring and Autumn Period, roughly 722BC to 481BC] political events". Of course, there are several other key figures that were also excluded from the Tso chuan but were to known to exist, so Sun-zi's exclusion from that work is not necessarily indicative of anything. Sun-wu is mentioned in passages in later works, though not to the extent of details necessary to paint a full portrait of his life. Worse is that those works only mention "Sun" - naturally, they could've been referring to any other famous people named Sun in the military/political context.

There is also the suspicion that the two biographical sources above (Shih chi and Spring and Autumn annals) have uncertain origins, at least as far as the versions available to us are concerned. Given that some 2000 years separate now and when they were supposed to have been written, there is the possibility that instead of being completely separate books, one merely referenced the other, with errors introduced along the way.

Edit: all this say that OP's question, as written, is difficult to conclusively answer. A better question would be "What do we think we know about Sun Tzu as a person?"

Sun Tzu (Sun Wu) was born around 545BC in the Spring and Autumn period (for the uninitiated, this period is named after a historical text, and has nothing to do with seasons. This period is the one of two halves of Eastern Zhou dynasty, the latter half being the Warring States) in the State of Qi. He was born to a noble household who's had a history of having military generals and strategists. His name, 武 (wu), gives the impression of war, but in fact it's actually made up of two sub-characters: stop, and spear, i.e. to stop conflict - the aspirations his father had for him. Growing up in such a household, he naturally had an interest in militaristic strategies and what not. He loved reading previous military texts (The Art of War is obviously the most famous, but it was not the first of its kind) and hearing tales from the battlefields. He'd show great intelligence and natural talent over the years, becoming an expert archer and carriage rider as well.

His career really started when he moved to State of Wu (吴, not to be confused with his name. They're not related), recommended by Wu state general Wu Zixu. The King of Wu read over Sun's Art of War, but didn't take it or him very seriously. He half-jokingly asked him to train his concubines. The concubines naturally though it was a joke and were fooling around. When nothing changed after Sun explained his expectations twice, he called for the head of two of the King's favorites. The King tried to call him off, but he insisted and had them beheaded. The concubines instantly conformed to Sun's directives. The King realizes that Sun is the real deal. And thus began Sun's official military career in the state of Wu. He'd work with Wu Zixu to help Wu achieve great success over rivaling states, over the reign of two Kings. The new King, after avenging his father's death, became complacent. In the end, Wu Zixu was forced to suicide, and had his body tossed into a river. Sun saw that this would probably be the end of Wu (the State). He hid away and revised the Art of War to what we'd know it as today. He passed away sometime around 470 BC.

Could Sun Tzu be one name credited for the words and works of a few authors the way scholars believe the writings of Homer are quite probably those of more than one writer?