Robert Caro is famous for colossal biographies of colossal figures. “The Power Broker,” his Pulitzer Prize-winning life of Robert Moses, weighed in at nearly 1,300 pages. His as-yet-unfinished biography of Lyndon B. Johnson — he likes to call the volume-in-progress “the fifth of a projected three” — totals 3,444 pages and counting.

The books are already monumental. And now Mr. Caro is getting monumental treatment himself.

The New-York Historical Society has acquired Mr. Caro’s papers — some 200 linear feet of material that will be open to researchers in its library. And just as important to the 84-year-old Mr. Caro, it will create a permanent installation in its museum galleries dedicated to showing how he got the job done.

“It’s like a true weight has been lifted from my shoulders,” he said last week in his office off Central Park West, where he was surrounded by hulking filing cabinets, piles of heavily scribbled-on legal pads and — tantalizingly — a wooden box holding typed pages of the eagerly awaited final Johnson volume.

In discussing the plans for the permanent exhibition, he repeatedly stressed the permanent part.

“With most archives, there’s a big splash, then two or three months later, it’s time for the next,” Mr. Caro said. “But I wanted something that wouldn’t go away.”