Wednesday is a big day in Congress: The man behind the Mueller Report is finally set to speak publicly, at two separate hearings. We asked our colleague Noah Weiland what we should expect:

When Robert S. Mueller III testifies on Wednesday, it’ll be his 89th time — 89th time! — as a congressional witness, which is among the most of any official ever. He despises the routine: the pontificating non-questions, the attempts to draw him into conflict and the length of the hearings. He’ll be in the witness chair for five excruciating (to him, at least) hours.

For an article about his history as a witness, I picked through hours and hours of dry back-and-forths over often mundane oversight questions (thank you, C-Span). It turns out that 12 years of leading the F.B.I. through a post-9/11 world yielded plenty of insight into the kind of witness Mr. Mueller is.

Here are three takeaways from my reporting on what we can expect Wednesday:

1. Mr. Mueller mostly testified in the courtly Senate, and in a deferential environment, which is not what the current House Judiciary Committee is known for. Mr. Mueller happens to know a lot of the faces he’ll encounter on Wednesday — he won’t be happy to see Representatives Jim Jordan and Louie Gohmert again — but he simply doesn’t have experience weathering the political tinderbox of Trump’s Washington. Wednesday will be completely unlike any of his other 88 appearances.

2. It’s a timeworn cliché that Mr. Mueller is “by-the-book.” Watching the footage, I saw a more revealing character trait, which was his conflict aversion in public. He’d rather go quiet than argue in the way two humans might when they disagree. In private, he could be different. John Pistole, the former deputy F.B.I. director, told me he once saw Mr. Mueller light into a member in an impromptu meeting on Capitol Hill. “I wish I had a video of it,” Mr. Pistole told me.

3. Keep sober expectations. Mr. Mueller’s final act in public life might be the anticlimax. He’s already a retiree, and he’s made it clear he doesn’t want to testify. On Wednesday, he’ll try to avoid making news. Matthew G. Olsen, Mr. Mueller’s special counsel at the F.B.I., put it this way to me: “As he might have advised a witness when he was a criminal prosecutor: Don’t go beyond the answer.”