“Сирота казанская” (The orphan of Kazan) such is the name given to people who can't help complaining about everything, especially about how hard their life is, often without any reason. Сирота – это ребёнок, оставшийся без родителей (orphan is a child left without parents). Such children should be under the care of the State, they usually live in “детский дом” (children's house), but before these houses used to be called “сиротский приют” (orphanage or orphan asylum).
But why do we have the expression “Сирота казанская” (orphan of Kazan)? И почему это определение вызывает ироническое отношение? (and why this definition has carries such a ironic attitude?)
The city of Kazan in ancient times был столицей Орды (was the capital of the Golden Horde), a state founded by the Mongols. They are know for the countless wars and conquests from the Southeast Asia to Europe in the 12th and 13th centuries. Since the beginning of the 13th century until 1480, Русь находилась под игом монголо-татар, платила им огромную дань (Russia was under the yoke of the Mongol, and paid a enormous tribute).
But even after the end of the invasion, the Mongol troops would frequently attacked Russian cities or merchants' caravans. Ivan the Terrible decided to put an end to it, and in 1552 he sent his army to Kazan, conquered it and annexed it to Russia, together with part of o the Mongol-Tartar state.
Many Khans (Tartar princes), fearing the terrible Tsar, began to search his favours. Они отказывались от своей веры (they renounced their faith) and принимали русскую веру (took the Russian faith) instead, they sent letters to the Tsar, жаловались на свою горькую жизнь (complaining about their hard life), сообщали царю о своём крещении (told him about their baptism), and просили у него милости (asked him for mercy). This, of course, brought disbelief and laughter to the Tsar.
And this is how the expression appeared.