Ex-presidents earn a lot of money from speeches; when did that start?

Returning to the public stage this week in Chicago, former President Barack Obama urged young people to get involved in politics. That appearance was unpaid. A scheduled speech for Wall Street firm Cantor Fitzgerald this September is not. The 44th president will reportedly receive $400,000 for the appearance at a health care conference. 

Baruch College Dean of Public and International Affairs David Birdsell said the upcoming speech is controversial because Obama was often a critic of Wall Street on the campaign trail and during his presidency.

While Obama is taking heat from both Republicans and Democrats for the decision, he is hardly the first former president to take on lucrative speaking engagements. Birdsell said it is "par for the course," adding that it was rarely a practice until Gerald Ford, the 38th president, began accepting high fees for speeches after the end of his presidency.

Ford earned fees in the tens of thousands of dollars. By comparison, Ronald Reagan once earned $1 million for a speech to a Japanese company. George W. Bush has given more than 200 speeches since 2009 and is paid $100,000 to $175,000 each, according to Politico. The all-time leader, though, is Bill Clinton. The Washington Post found that Clinton has earned close to $105 million for more than 500 speeches since 2001. Former First Lady Hillary Clinton is also cashing in. The former Democratic presidential nominee's ties to Wall Street frequently haunted her campaign.

But not every first family has seen mountains of green. Former President Jimmy Carter has volunteered for Habitat for Humanity, served as an election observer overseas, and gone on humanitarian missions, Birdsell said.

Sitting presidents earn $400,000 a year. Ex-presidents have a $200,000 a year pension and additional money for office space and staff.