beggar on horseback
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a beggar on horseback
One who has become unscrupulous or irresponsible due to the sudden acquisition of wealth. The phrase alludes to several related proverbs, such as "give a beggar a horse and he'll ride it to death" and "set a beggar on horseback and he'll ride to the devil," which suggest that an unexpected windfall is often misused or squandered. I'm not surprised to hear that he's broke again—he always seemed like a beggar on horseback.
beggar on horsebacka formerly poor person made arrogant or corrupt through achieving wealth and luxury.
Compare with the mid 17th-century proverb set a beggar on horseback and he'll ride to the devil , meaning that a person not used to power will use it unwisely.