In many ways, Mr. Buffett has portrayed himself as the business world’s guardian of homespun values — decrying fat paychecks for executives, shunning technology stocks because he didn’t personally understand the businesses, and criticizing tax policies that encourage trading of stocks rather than the patient buy-and-hold approach he favors.

In his personal life, however, Mr. Buffett has been less conventional. His first wife, Susan, left the family home in Omaha in the late 1970’s, after raising the couple’s three children, and moved to San Francisco.

And she introduced a friend, Ms. Menks, to her husband and encouraged Ms. Menks to take care of Mr. Buffett.

The two women had become friends at an Omaha restaurant where Susan Buffett sang and Astrid Menks seated patrons.

“Unconventional is not a bad thing,” Susie Buffett said. “More people should have unconventional marriages.” She said her mother, who was also known as Susie, wanted to be known for who she was, especially as her father’s wealth and fame grew.

“She basically wanted a room of her own. They were very connected in a very deep way,” speaking frequently on the telephone and traveling together, Susie Buffett said. “They didn’t need to be in the same room.”

“Astrid and my mother were very close — really loved each other,” Susie Buffett said.

In an interview with Charlie Rose shortly before her death, the first Mrs. Buffett said of Ms. Menks’s relationship with her husband: “She takes great care of him, and he appreciates it and I appreciate it. She’s a wonderful person.”