WASHINGTON — Most Friday nights as he conducted his investigation, Robert S. Mueller III drove seven miles from his offices by the Capitol to Salt & Pepper, a dimly lit, mostly empty restaurant near his home, settling into a wooden booth partly covered by a dowdy red curtain.

The ritual — usually undertaken with two friends, a glass of white wine, a plate of scallops and no security detail — was perhaps the most public contrast to the way Americans came to know Mr. Mueller in his 22 months as special counsel: as a partisan symbol more than a person, his name synonymous with whatever they wanted to believe about President Trump and American law enforcement, their hopes and fears stashed in the pockets of his pinstripe suits.

Throughout his investigation, Mr. Mueller chose to remain silent, the rare recluse in a world rife with Twitter battles and talking heads. But now, with his report filed, Congress clamoring for more of his findings and a polarized public picking over the remains of his work, the tight-lipped Vietnam veteran and former F.B.I. director, who will be 75 in August, remains a figure of mystery and fascination.

The post-report spotlight may prove to be a new test. On Sunday, before his findings were revealed for the first time, a usually photo-shy Mr. Mueller drew a gawking crowd outside St. John’s Church near the White House, where he attended morning services, a visit that allowed for some of the first pictures of him since he was appointed special counsel in May 2017.