The generals mentioned are:
Field Marshal William Slim, commander of the 14th Army in WW2 (known as "the forgotten army" it beat the Japanese in Burma; Slim has a good claim to be the best general of WW2).
Field Marshal Bernard Montgomery, know as "Monty" commanded British Forces at El Alamein and in the Normandy campaign. He was once described to me by Field Marshal Michael Carver as "a shit".
Field Marshal Alan Brooke (Viscount Alanbrooke) was Chief of the Imperial General Staff during WW2, making him Churchill's chief military advisor. He was highly critical of Churchill in his post-war memoirs.
Field Marshal Douglas Haig commanded the British Expeditionary Force from 1915 to 1918. A controversial figure, many (including Churchill and Lloyd George) blamed him for unimaginative strategy and excessively bloody campaigns, with Passchendaele and the Somme being criticised in particular. There's been an attempt by revisionist historians to rehabilitate his reputation in recent years.