beggar a person who lives by asking for money or food.
beggar on horseback a formerly poor person made arrogant or corrupt through achieving wealth and luxury; recorded from the early 16th century. The phrase is related to the late 16th century saying, set a beggar on horseback and he'll ride to the devil, meaning that a person unused to power will make unwise use of it.
The Beggar's Opera is a low-life ballad opera (1728) by John Gay (1685–1732), combining burlesque and political satire in its story of the highwayman Macheath who is betrayed by the informer Peachum. In the 20th century, Bertolt Brecht's version of Gay's work, The Threepenny Opera (Die Dreigroschenoper, 1928) was one of the theatrical successes of Weimar Germany.
beggars can't be choosers someone who is destitute is in no position to criticize what may be offered. Saying from the mid 16th century, which in its original form ran, ‘beggars should not be choosers.’

beg·gar / ˈbegər/ • n. 1. a person, typically a homeless one, who lives by asking for money or food.2. inf. a person of a specified type, often one to be envied or pitied: poor little beggars.• v. [tr.] reduce (someone) to poverty: by being soft to the unfortunate, we beggared ourselves.