Short answers, pulled from the story.
The foundation of the Tower of London dates to 1066 when William the Conqueror ordered its construction following his victory at the Battle of Hastings. Work on the White Tower which gives the castle its name began in 1078 and was likely completed by 1100.
William made Gundulf Bishop of Rochester responsible for the construction of the White Tower between 1078 and 1087. The White Tower is recognized as the earliest stone keep in England and served as the strongest point of the early castle.
The Tower of London was besieged for the first time in its history in October 1191 when forces loyal to Prince John attacked the fortress held by William Longchamp. Longchamp capitulated after just three days deciding he had more to gain from surrender than prolonging the siege.
Eleven men were tried in private and shot by firing squad at the Tower of London for espionage during the First World War. During the Second World War the last person to be executed at the Tower was German spy Josef Jakobs who was shot on the 15th of August 1941.
King John who reigned from 1166 to 1216 first started keeping wild animals at the Tower of London with records showing payments to lion keepers in 1210 and 1212. The tradition continued through Henry III's reign which lasted from 1216 to 1272 including a polar bear gift from Haakon IV of Norway in 1252.