Every time Larry Gibson thinks he’s left the political game for good, he somehow gets pulled back in.

A few years ago, it was a presidential campaign in Madagascar. Most recently, he found himself signing onto a letter along with hundreds of other former federal prosecutors who asserted that if Donald Trump were not president, he would be charged with obstruction of justice based on evidence in the Mueller report.

“I am done now,” he said, sounding as if he doesn’t quite believe himself.

Some things you just don’t get out of your blood. For Mr. Gibson, politics is just one of those.

The 77-year-old was born in Washington, D.C., but grew up in racially segregated Baltimore, and he has worn many hats that have influenced and continue to influence the political landscape of Baltimore and elsewhere, shape the careers of countless attorneys and judges and chronicle the history of African Americans. Attorney, law professor, mentor, author, photographer, activist and collector of civil rights memorabilia. The list of roles is long for Mr. Gibson.

“You have to recognize that this guy is a force,” said Donald B. Tobin, dean and professor of the University of Maryland Francis King Carey School of Law, where Mr. Gibson has long taught. “Larry is part of a group of figures in our history who were coming alive in transformative times. Larry came up during a time when we were transforming from a racist country to a country that was crying out for people like him who were helping us understand each other. He helped the black community in Baltimore recognize its voice.”

Mr. Gibson’s first dabble in politics came in high school, when he was elected the first African American class president at City College, not so long after the Supreme Court ordered the desegregation of schools. Attending the school on the other side of town opened his eyes to part of life he never saw in his poor, black neighborhood. While at Howard University, where he was also class president, he ran one of his first campaigns for a candidate for homecoming queen.

It didn’t take long for bigger campaigns to come his way and for Mr. Gibson to become one of Baltimore’s most powerful political operatives. He played a part in some of the area’s most notable and historic elections, including running campaigns that led Kurt Schmoke to become the first elected African American Baltimore mayor and, in a separate election, Milton Allen the city’s first black state’s attorney. He even took his talents abroad, securing a victory for Liberia’s first female president, who was also Africa’s first female head of state. And that’s just a few examples.

“He is responsible for the African American leadership in this city, particularly when it comes to the legal profession,” says Baltimore solicitor and former federal judge Andre Davis, one of many who came up under Mr. Gibson’s tutelage. “He is the father, the grandfather and the uncle. When he got Kurt Schmoke elected, nobody saw that coming. It was groundbreaking and transformative.”

Congressman Elijah Cummings first met Mr. Gibson as a 17-year-old City College student when he was tasked to find people to induct into the high school’s hall of fame. That evolved into a mentorship and then friendship so close that Mr. Cummings still turns to him for every major life decision.

“He is a real detailed kind of guy,” Mr. Cummings says. “He is very adept at reading polls, taking polling data and trying to decipher what it means and how it can help affect an election.”

As Mr. Gibson has tried to spend less time on politics, teaching and mentoring law students is still a passion. He was recently named the Morton & Sophia Macht professor of law at the law school.

But he’ll soon even take a bit of break from that to work on his second book about Thurgood Marshall. Next year he plans to take a sabbatical to physically trace the steps of Marshall’s early law career, with plans to travel to states such as Oklahoma, Texas and North Carolina. He has even identified physical places where the judge from Baltimore once stayed. Mr. Gibson has been collecting information on Marshall since meeting him in 1975.

“Maybe I was a natural historian,” he said.

Yet another role that puts Mr. Gibson in the history books in his own right.