the ruin of (someone or something)
The cause of someone's or something's failure, destruction, or downfall. The disastrous product proved to be the ruin of the company after moving less than a quarter of a million units. Many assumed the scandal would be the ruin of the candidate.
ruin of someone or something
the cause of destruction; a failure. Your bad judgment will be the ruin of this company! The greedy politicians were the ruin of the old empire.