What is the largest or most "prestigious" advertising company?

I know this sounds like a trivia question haha, but I was wondering what is the largest or most "prestigious" advertising company. I know that companies advertise themselves, but are there companies whose sole purpose is to advertise for products? And if so, which one is well-known? Thanks so much in... show more I know this sounds like a trivia question haha, but I was wondering what is the largest or most "prestigious" advertising company. I know that companies advertise themselves, but are there companies whose sole purpose is to advertise for products? And if so, which one is well-known?

Thanks so much in advance!
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