(Reuters) - What's the difference between a mosquito and a lawyer? One is a blood-sucking parasite, the other is an insect.

Why won't sharks attack lawyers? Professional courtesy.

How do lawyers sleep? First they lie on one side, then they lie on the other.

Lawyers don't get a lot of love. But for every nasty joke and negative stereotype, there's a counterweight: pro bono

I'm aware of no other profession that imposes a similar ethical expectation on its members to work for free. Yes, doctors and architects and accountants and engineers and other professionals routinely donate their services to worthy causes.

But they don't shoulder an obligation like the American Bar Association's Model Rule 6.1: "Every lawyer has a professional responsibility to provide legal services to those unable to pay. A lawyer should aspire to render at least (50) hours of pro bono publico legal services per year."

This week is Pro Bono Week, an annual celebration by legal organizations across the country.

In that spirit, I'm kicking off a new monthly feature for this column: Pro Bono Heroes. The goal is to recognize and celebrate extraordinary pro bono work by a law firm, corporation or lawyer, highlighting one champion at the end of every month. (Please feel free to email me suggestions going forward!)

The inaugural crown goes to Jenner & Block, which last week announced a pledge to donate $250 million in legal services over the next five years. The yearly total — about $50 million — is more than 10% of the firm's most recent annual gross revenue.

Pro bono is "a defining feature of us as a firm," said co-managing partner Katya Jestin, noting that the 500-lawyer Chicago-founded firm traces its commitment to pro bono back to the 1950s, three decades before the ABA first included an explicit public service provision in its ethical rules.

Over the years, the firm has been a pro bono leader, routinely at the front of the Big Law pack.

Given this history, the $250 million commitment doesn't come from left field. But even for Jenner, it's an ambitious pledge —and one that firm leaders expect will entail upping the already substantial pro bono caseload.

"We never assigned a dollar value to our efforts before," co-managing partner Randy Mehrberg told me. "However you slice $50 million [a year], it's a huge number."

In my mind, it's also more powerful (especially to non-lawyers) than simply reporting that firm lawyers last year donated an average of 170 hours of pro bono work — and a combined total of 1.6 million hours over the last 30 years.

The firm will use each lawyer's standard hourly billing rate to calculate the value of the services.

I asked the two co-managing partners if making the $250 million commitment was a hard sell to the partnership.

They laughed. "There was zero opposition," Mehrberg said.

Jestin added, "We're a self-selected group, a coalition of the willing. People choose Jenner & Block because of who we are culturally," she said. Jenner lawyers "are not chasing the last dollar" at the expense of public service.

If anything, she continued, the partnership is apt to be "more upset if we failed to live up to our (pro bono) obligations than if we didn't make budget."

Jenner's profits per equity partner last year were about $1.6 million, according to The American Lawyer.

Firm lawyers have wide latitude to choose pro bono matters to work on, including high-impact litigation, individual criminal cases and transactional work such as nonprofit 501(c)(3) formations. "So long as the case meets the ABA definition of pro bono, we support it," Jestin said.

A few ongoing matters give a sense of the scope.

For example, litigation department co-chair David Bradford is co-counsel on a case with the MacArthur Justice Center against the U.S. Postal Service, the U.S. Postmaster General Louis DeJoy and President Donald Trump on behalf of a group of organizations in Florida concerned about ballot delivery.

Meanwhile, Susan Kohlmann is serving as lead partner in class action litigation on behalf of thousands of Navy and Marine Corps veterans denied an honorable discharge when dismissed from the military with post-traumatic stress disorder, traumatic brain injury or military sexual trauma.

Partner Alison Stein is leading a team representing Planned Parenthood of Wisconsin in a case challenging certain abortion access restrictions, and partner Precious Jacobs Perry has worked with the Chicago Alliance Against Sexual Exploitation on a human trafficking case.

Jenner lawyers have also teamed up with Lawyers Without Borders to offer ongoing legal guidance on international human rights, animal trafficking and other global legal issues, staffing six different projects on four continents.

In addition, firm lawyers have helped exonerate seven people for wrongful convictions and represented protestors who were arrested without cause in the wake of the George Floyd protests earlier this year.

Given increasingly pressing social justice issues and the widespread need for access to legal services, Jestin said it was "the right time" to go big on pro bono. "We are doubling down on our commitment," she said. "We hope other firms double down too."