Short answers, pulled from the story.
The name Ultra originated from a new designation adopted by British military intelligence in June 1941 for wartime signals intelligence. This term became standard among western Allies because the intelligence obtained was considered more important than the highest existing classification known as Most Secret.
Key people responsible for success against Enigma included mathematicians Alan Turing and Hugh Alexander along with chief engineer Harold Keen. Marian Rejewski and the Polish Cipher Bureau first broke German military Enigma in December 1932 before handing reconstructed machines to French and British forces on the 25th of July 1939.
Ultra intelligence provided advance warning of bombing raids during the Battle of Britain through teleprinter links between Bletchley Park and RAF Bentley Priory. An Ultra message reported equipment loading planes and paratroops gear dismantled on the 17th of September 1940 which led to the cancellation of Operation Sea Lion.
Lorenz SZ 40/42 machines codenamed Tunny by British codebreakers produced high-level strategic intelligence sent between Wehrmacht high command OKW. This work was more difficult than Enigma since British codebreakers had no knowledge of the machine producing it but eventually used Colossus computers to penetrate these systems.
A thirty year rule meant no official mention of Bletchley Park existed until the mid 1970s when the secrecy finally ended. Churchill requested recipients of Ultra intelligence not divulge source information after V-E Day on the 25th of May 1945 to prevent damage to future operations or Axis blame for their defeat.