Nancy Reagan, the stylish and influential wife of the 40th president of the United States who unabashedly put Ronald Reagan at the center of her life but who became a political figure in her own right, died on Sunday at her home in Los Angeles. She was 94. The cause was congestive heart failure, according to a statement from Joanne Drake, a spokeswoman for Mrs. Reagan. Mrs. Reagan was a fierce guardian of her husband’s image, sometimes at the expense of her own, and during Mr. Reagan’s improbable climb from a Hollywood acting career to the governorship of California and ultimately the White House, she was a trusted adviser. “Without Nancy, there would have been no Governor Reagan, no President Reagan,” said Michael K. Deaver, the longtime aide and close friend of the Reagans who died in 2007.