The Fairbairn-Sykes fighting knife was developed as a joint effort between William Fairbairn, Eric Sykes and John Wilkinson. The two former men of the Shanghai Municipal Police force and British Army the latter of the Wilkinson Sword Company.
I’ll not go too far into the history and development of the knife here as this is adequately covered in other places. A lot of the aspects of the design were carried over from the work of Fairbairn and Sykes on their Shanghai fighting knives-developped during their time with the police there. Each one was handmade and different to the next one.
Fairbairn was experienced in fighting with knives and knife fighting, having been on both ends innumerable times working in Shanghai. From this experience he developed what he called his ‘timetable of death’. I think it wouldn’t be unreasonable to say that a man so studious in fighting is best qualified to design a knife so single-minded in its purpose.
On their return to Britain, they developed the knife further with the Wilkinson Sword Co. In November 1940, the War Department ordered a small number of knives to be delivered.
Over the next five years of war, Wilkinson produced three patterns of the FS knife for use by British and Allied forces while Fairbairn and Sykes trained them in their use. Royal Marines, Army Commandos, Royal Navy Commandos, the SOE and many others benefitted from their experience.
The knife was so popular it ended up featured on the insignia of Commando Units not only in the UK but in countries all over Northern Europe. It is still in use today worldwide.
To read up more on the design of this weapon, I recommend this site, which is overall quite thorough.
For more about the use of knives, this page has some interesting information.