Ms. Fitzpatrick began her career at O’Connor & Associates, the Chicago firm that was later acquired by UBS as the Swiss bank’s internal hedge fund. She rose to lead the firm and become one of Wall Street’s most powerful women. Now, largely unknown outside the industry, Ms. Fitzpatrick faces her biggest and most public challenge yet: working for George Soros, the estimable octogenarian investor and philanthropist. Last Monday, she started as chief investment officer of Soros Fund Management, which manages around $26 billion of Mr. Soros’s personal and family wealth. In taking the job, she follows in the footsteps of finance legends including Keith Anderson, a co-founder of BlackRock, and Stanley Druckenmiller, the billionaire investor. Even Steven Mnuchin, the new Treasury secretary, was once brought in to open a lending business. Since Mr. Druckenmiller left the firm in 2000, Soros Fund Management has churned through eight chief investment officers. It’s a remarkable turnover for the top of any company, even among hedge funds, which are known for a cutthroat culture. Though Ms. Fitzpatrick is registered as a Republican, she appears unfazed that her investing acumen will in turn support Mr. Soros’s activism. Born and raised in Irvington, N.Y., Ms. Fitzpatrick was the middle child among five siblings who grew up in a cul-de-sac on a street bustling with young families. After graduating from the University of Pennsylvania’s Wharton School with a bachelor of science degree in 1992, Ms. Fitzpatrick landed a job with O’Connor & Associates as part of a junior group of American Stock Exchange clerks. She moved on to trade options for O’Connor at the Chicago Board Options Exchange.