When the colonies declared their independence from Britain, Thomas Grimball Jr. intended for them to succeed.

The Charleston resident — an attorney and planter — loaned the South Carolina government money to operate. And when the British laid siege to the city in 1780, he commanded troops in its defense. He was an important supporter of the Patriot cause.

Today, however, he is largely forgotten by history.

On Wednesday — Independence Day — the Old Exchange Building begins its campaign to change that.

At 1 p.m., the Exchange will unveil a portrait of Grimball donated by his descendent Paul Grimball Marshall Jr. and the Marshall Family Trust, which is also financing an upcoming permanent exhibit at the museum.

“Thomas Grimball is a forgotten founder,” said Tony Youmans, director of the Exchange. “I believe if he had lived, he would have been South Carolina Senator Grimball, or Governor Grimball.”

Grimball was descended from one of the first families to settle Charles Town in 1680. By the time he was 20, he had become an influential local resident. He was an attorney and married the daughter of Samuel Prioleau.

Eventually he became a state lawmaker and held positions with Chancery Court and the Charleston Library Society.

In the 1770s, he became commander of the Charles Town Battalion of Artillery, and led the procession from the state house to the Exchange Building when the Declaration of Independence was read here for the first time.

In 1779, he used his personal wealth to loan the state 80,000 pounds in South Carolina British Sterling to keep the fledging government operating. And when the British began its siege of Charles Town the next year, Maj. Grimball’s Battalion of Artillery fought them off from the fort that stood where Marion Square is today.

A portion of that tabby fort remains in the spot.

Grimball was a man of such stature that, during the siege, Thomas Heyward and Edward Rutledge — both signers of the Declaration of Independence — reported to him.

“He risked everything for this country’s independence,” Youmans said.

When the British finally took Charles Town, Grimball was arrested and imprisoned for a year in St. Augustine.

Upon his return, Grimball served as sheriff of the city until his untimely death — the cause is lost to history — at 39. He is buried in the family vault at St. Philip’s Episcopal Church.

Paul Grimball Marshall Jr. — known as “Sonny” to many locals — said he commissioned this painting of his famous ancestor after learning more about his life. Marshall said that perhaps Grimball has remained under the radar for so many years in part because he had no children to keep his memory alive.

Local artist Charles DuPre DeAntonio — son of painter Charles DeAntonio Jr. — depicted Grimball as he looked during the Siege of Charles Town. While Marshall will keep a copy, the original will hang on the Exchange floor at the Old Exchange Building and Provost Dungeon.

“We’re going to take him back over to the Exchange Building and hang him,” Marshall joked, referring to his ancestor’s one-time prisoner-of-war status. “He is kind of looked over, but he is a lost patriot.”

If local historians have anything do with it, Thomas Grimball will no longer be lost to history.

Reach Brian Hicks at 843-937-5561 or follow him on Twitter at@BriHicks_PandC.