Though he is mistrusted by a number of Republicans, Lew has some bipartisan credentials that might help him in budget talks.
The one-time Citigroup executive honed his political skills as a policy adviser to Democratic House Speaker Tip O'Neill, who is touted as a symbol of bipartisanship because he worked with Republican President Ronald Reagan to change the tax code and the Social Security retirement program in the 1980s.
"Jack is more concerned about what's fair than any personal attention or credit," said Pamela Jackson, who worked with Lew when O'Neill was speaker. "He was an integral and important part of those (tax policy and Social Security) negotiations as a trusted adviser to the speaker," she said.
Lew is an orthodox Jew and observes the Sabbath holiday, which requires him not to work, including answering phones, between Friday evenings and sunset on Saturday. Lew has said he is available to work in emergencies on Saturdays and does not view doing so as a violation of his faith.
During Obama's re-election campaign, Lew campaigned for the president among Jewish constituents in Florida.