Which major collector had the largest collection?

Perhaps Louis Eliasberg? He not only had U.S. coins, but a lot of foreign coins as well. Or King Farouk of Egypt
? People today forget this King being a major coin collector. It says in this article: https://scvhistory.com/scvhistory/signal/coins/soltaylor021608.html
that he had over 8,500 U.S gold coins alone!

Wow... 350,000 coins.... that is huge. I would assume, with that quantity, there were a few favorites that the collector would have kept accessible. Far too many for me to consider....Cheers, RickO

Brand

I can't think of anyone either. Other CCC hall of farmers:

Hall of Fame
– Chicago Coin Club –

The first monthly meeting of the Chicago Coin Club was held in February, 1919. In honor of the centennial of the Chicago Coin Club, the club created a Hall of Fame to recognize some of the prominent numismatists among its ranks over the past century. Twelve inductees form the Inaugural Class, with one member announced each month during 2019.

1. J. Henri Ripstra
2. Dr. Alexander Michaels Rackus
3. William Forrester Dunham
4. Virgil Michael Brand
5. M. Vernon Sheldon
6. Lee Francis Hewitt
7. Harry X Boosel
8. Glenn B. Smedley
9. Elston G. Bradfield
10. Arlie R. Slabaugh
11. Harry Flower
12. Charles J. Ricard
    After the inaugural class of twelve has been named, the criteria for future membership shall be listed here, along with some mention of the committee responsible for nominating new members, the voting on the nominees, and all of the other tasks in support of this endeavor.

I suspect Virgil Brand had the largest collection by a wide margin. He may even have challenged or beaten Scrooge McDuck's money bin in terms of number of pieces.