He was first mentioned by Robin during the initial encounter with Aokiji. Because of his actions, Kizaru can be considered the secondary antagonist of the Sabaody Archipelago Arc and Marineford Arc.
Kizaru is an incredibly tall man, roughly the same size as the other two former admirals Aokiji and Akainu. Kizaru is a middle aged man with a moderate amount of wrinkles on his face, black hair, and a very thin beard. He looks and is in fact older than the other two admirals.
His standard outfit consists of a yellow striped suit with a Marine coat draped over his shoulders like a cape, his arms not in its sleeves. Kizaru also wears pure white shoes, gold-amber tinted sunglasses, and a dark green shirt with a mauve tie under his yellow suit. There is a tiny Black Den Den Mushi on his left wrist, like a wristwatch, underneath the sleeve of his suit. He is generally seen wearing a relaxed grin on his face.
As a child he wore a large yellow striped hat, much like his older self's suit, a yellow vest and he still had his grin that he maintained through out his life. In his early days as a Marine he wore a knit cap with the Marine emblem on it, sunglasses and also a normal Marine jacket with a striped undershirt.
In his youth, he wore a Marine skull cap and he had no facial hair.
Twenty-seven years before the start of the series, he wore a typical Marine cap and his beard was not as full as it is currently. He also lacked the gold amber-tinted sunglasses, shirt, and tie, which he was last seen wearing.
When he was seen stationed at Marineford as a Vice Admiral thirteen years before the start of the series, he was sporting a large dark grey hat, dark gloves and had a cigarette in his mouth. His trademark pinstriped suit was light grey, matching his tie, while his thin beard was missing.
After the timeskip, he switched out his inner shirt and tie for a dark green turtle neck and chose a suit with a different striping pattern.
Kizaru seems to be very laid-back and easygoing, speaking rather slowly and occasionally drawing out the last word of his sentences, which is strange considering this behavior is in direct contrast with his Devil Fruit power. He takes everything lightly regardless of the severity of the moment. In surprising, perilous and unexpected situations, he is apparently never shocked and even when a pirate fired a bullet at him, he seemed to be focused only on calling his subordinate. He even asked the offenders where his subordinate was. After uprooting a mangrove tree, he laughed to himself that the force he used was a tad excessive.
He is also completely calm and cool-headed, even in tense situations, such as when Basil Hawkins appeared unharmed by his attack, or when Silvers Rayleigh appeared. He speaks in a politely sarcastic manner and is very mocking towards his enemies, such as mocking Luffy for being too weak. He often taunts and belittles his foes in and out of battle, such as taunting Whitebeard about Luffy being too feeble to lead the charge towards the execution platform.
Unfortunately for the World Government, he can be quite absent-minded and irresponsible, judging by the fact he used a lot of power in a kick directed at the escaping pirates, knocking down the surface part of a Yarukiman Mangrove tree, and tried to call Sentomaru with a black Den Den Mushi, which is only used for intercepting communications. He also seems to prefer his own name, Borsalino, rather than his alias.
After Luffy sent Charloss flying during the Sabaody incident, Kizaru volunteered to be dispatched by Sengoku to deal with the nobles' predicament, partly to fulfill his duty as an admiral and because he was under the impression that a trip down to the Archipelago to expel the pirate threat would be mostly relaxing and was seemingly disappointed when Silvers Rayleigh came out to confront him.
If nothing else, Borsalino appears to be more lax than Aokiji, such as when Luffy, Jinbe and Law escaped from Marineford, he completely dropped the matter, his attitude regarding it being that of a carefree reaction.
However, he has shown his ruthlessness. While he never has expressed any sympathy for or against the philosophy of Absolute Justice, Kizaru's careless behavior shows very little mercy towards his enemies, particularly pirates whom he has targeted. Kizaru even decided to apprehend Silvers Rayleigh, who had retired from piracy over twenty years earlier, simply because, as a member of the Roger Pirates, his crimes could not be forgiven. Following the events of the Sabaody Archipelago, Kizaru arrested 500 pirates. Also, he sees the Shichibukai as nothing more than pirates, even if they are on the World Government's side. Even when Little Oars Jr. was bloody and dying after having lost a leg, Kizaru showed no mercy and simply offered to go ahead and shoot Little Oars Jr. through the head. As revealed by the author, his motto is "unclear justice"
Kizaru often comments that some of the abilities of his opponents are quite frightening. One instance was after he witnessed the Devil Fruit abilities of three Supernovas, he referred to them as monsters, although he was otherwise unfazed by them. Another was after he tried to directly attack Whitebeard, First Division Commander Marco intercepted his attack with ease which made Kizaru point out how scary the Whitebeard Pirates were. When Luffy was launched towards the execution platform and stood before all three admirals, Kizaru commented that this youth was "scary".
The most recent occurrence was when Benn Beckman aimed a gun at him, although in that case Kizaru said it sarcastically and still succeeded in getting in an attack while Beckman was shocked that he was not done yet. Since Kizaru always delivers such admissions of fear with a deadpan expression on his face and his usual lackadaisical tone of voice, it is never clear if he is mocking his opponents or if he is being serious.
It is shown, however, in his fight with Z that he is somewhat capable of fear, as he seemed scared when Z decided to unleash the power of the Dyna Stone, and even possibly terrified when it was about to literally blow up in his face.