Willie has a well-developed, if slightly dark, sense of humour, and often jokes about his and Modesty’s lifestyles. He is given to quoting psalms, as he was once imprisoned for a year in Calcutta with only a psalter to read. Very sociable, he has a number of female acquaintances from all social levels (as Modesty humorously describes them, „from premier cru to honest vin de pays„), and is often reminded of anecdotes of them in the most unusual situations (such as when swimming in shark-infested waters or when hauling heavy objects up slopes). The one exception to his romantic conquests is Modesty Blaise; feeling that he owes her a debt greater than anything physical can offer, he refuses to consider her in a romantic light and Modesty, in return, reciprocates by treating Willie as her one trusted friend. Willie rarely refers to Modesty Blaise by her name; his preferred nickname for her is „Princess“. On occasion, he literally provides a shoulder for her to cry on (one of Modesty’s character traits is that she occasionally weeps following the conclusion of a particularly nasty mission).
Willie Garvin is a tall and extremely strong man, though not heavily muscle-bound. He has a scar on his right hand made by a man named Suleiman, who was later killed by Modesty because he was torturing Willie. Like Modesty, he is a polymath of the first order: adept in safe-cracking and lock-picking, micro-electronics, expert at military tactics and a student of the criminal arts. He speaks several languages, including German, Spanish, Arabic and French; his English has a heavy cockney tone to it, though he is able to turn it on and off like a switch. Willie is a master knife thrower and can throw almost any object with extreme precision. He makes his own knives and is deadly with them at ranges up to 90 feet. He does not like pistols (because he thinks that guns give people too much confidence), and he and Modesty have also stated that he is a poor shot, but he has shown himself to be capable on the rare occasions that he uses such weapons. As an ex-soldier, he is skilled with rifles and submachine guns, and has on occasions also used a sniper rifle.
Willie, like Modesty, has a strong sense of right and wrong that is governed more by his morals than by the law. Although he avoids using deadly force whenever possible, usually taking his cue from Modesty as to whether to fight „for keeps“ (the duo’s euphemism for killing), he will not hesitate to kill to protect Modesty (see, for example, the conclusion to the 1975 comic strip „Cry Wolf“).
Willie and Modesty both smoke Gauloises (Sabre-tooth).