Alan Turing: Invented an electro-mechanical machine called the "bombe." The bombe was basically a series of Enigma machines wired together that could rapidly test various rotor settings to see whether or not the setting being analyzed could be eliminated as a possible solution.
F.W. Winterbotham: Winterbotham was involved with Enigma almost from the beginning at Bletchley Park. His main contribution to Enigma during the war was to establish and supervise Special Liaison Units (SLUs) that were attached to all of the main headquarters units for Allied ground and air forces. Relevant Enigma information would be relayed from Bletchley Park to the appropriate SLU via one-time-use code pads, a very secure mode of transmission. Then the SLU, following a very strict secrecy procedure, would pass-on the information to a tightly controlled group of officers at their unit for immediate action. By war's end, the system was working so well that, at times, the SLUs were delivering Enigma intercepts to their Allied commanders almost as fast as the Germans were getting the same Enigma message to their commanders.
Wing Commander Humphreys: "Humph," as he was called by his friends, was a British officer during World War II. Prior to WWII he had been a commercial salesman in Germany, and he was an expert in the language. In charge of Hut 3 at Bletchley Park, Humphreys' job was to take the German Enigma decrypts and translate them into English. It was Humphreys who, on September 17, 1940, realized the significance of an Enigma decrypt from Hitler authorizing the dismantling of aircraft loading equipment at Dutch airfields. Aircraft loading equipment was essential if Hitler planned to invade England. Dismantling the equipment meant that the invasion was cancelled.
The list is huge. Start with: Alan Turing and Hugh Alexander in Hut 8 (Naval). Next try Gordon Welchman and Stuart Milner-Barry in Hut 6 (Army and Air). Turing and Welchman were the joint designers of the concept of the Bombe based on an original idea from the Polish mathematicians, Rejewski, Zygalski & Roscyki. Add in Harold (Doc) Keen of the British Tabulating Machine Company who made Turing and Welchman's ideas into a workable machine. Don't forget Dilly Knox, John Jeffries and a mass more. This is all heavily documented on the Bletchley Park web-site and Wikipedia without repeating it all here. These are the people in the front-line of Enigma cryptanalysts. Winterbotham and Humphreys weren't as close.