Sun Tzu
Sun Tzu is an author.
Almost nothing about Sun Tzu is settled. He is described as a general, strategist and philosopher of the Eastern Zhou period, and tradition credits him with The Art of War, but scholarship places the earliest parts of that text at least a century after the life attributed to him. Sources give confident birth and death dates and they do not agree with each other, so the honest position is that a text exists and a biography largely does not.
What survives is the book, and for something this old its argument is unusually clear: fighting is the expensive way to win, terrain and an enemy's assumptions do more work than force does, and a commander reduced to improvising has already lost the important part. Its afterlife dwarfs its subject. It has been read as a manual by soldiers, executives, coaches and negotiators, which is why almost everything published under his name is one short text repackaged for a new shelf.
Books (4)
Where to start with Sun Tzu
Read The Art of War itself, and read it whole. It is short enough for a single sitting, and reading it straight through is the only way to notice how much of it is about avoiding a battle rather than winning one. The aphorisms that circulate on their own are the least interesting part.
The other three entries here are later packagings sold under his name rather than new material. The Art of War - a Samurai Master Class presents the ideas through a Japanese martial frame, while The Way of the Warrior and Spirit of the Warrior gather the same lineage for a general reader. They are worth your time only if you want the commentary and presentation, because the source text is already in your hands.