Wells Fargo Co. quietly passed a milestone at the end of trading last week: It’s now the most valuable U.S. bank ever, surpassing Citigroup Inc.’s 2001 record.

Wells Fargo closed Friday with a market capitalization of $285.5 billion, based on 5.19 billion shares outstanding on Oct. 31, according to data compiled by Bloomberg. That beats the previous record set by Citigroup on Feb. 5, 2001, when its value reached $283.4 billion, the data show.

Wells Fargo, which counts Warren Buffett’s Berkshire Hathaway Inc. as its largest shareholder, doubled its size in 2008 by outmaneuvering Citigroup to purchase Charlotte-based Wachovia Corp.

San Francisco-based Wells Fargo employs about 22,100 in the Charlotte area, its largest employee base. The lender made one of out every four U.S. mortgages last year and now oversees the most U.S. bank branches.

“Our focus is on doing what is right for our customers every day, and we are pleased our investors place their confidence in Wells Fargo,” Ancel Martinez, a bank spokesman, said in a statement.

Wells Fargo closed Monday at $54.77, down less than 1 percent, and the stock’s 21 percent gain this year tops the 7.7 percent advance for the KBW Bank Index of 24 U.S. lenders.

Berkshire’s stake in the San Francisco-based bank is valued at more than $25 billion, according to data compiled by Bloomberg.