WELLINGTON, New Zealand

“I CAN take you to see Fran now.”

At Stone Street Studios here, an expansive complex where the “Lord of the Rings” movies were made — and where Peter Jackson has spent the last two years deep in production on his “Hobbit” pictures — this is the equivalent of being invited behind the curtain to meet the Wizard of Oz.

Fran Walsh, a seven-time Academy Award nominee and three-time winner, was a co-writer of 12 of Mr. Jackson’s movies, including the blockbuster “Rings” trilogy, which sold almost $3 billion in tickets, and forthcoming “Hobbit” series. “Heavenly Creatures,” his breakthrough 1994 drama, was her idea. Warm and witty, Ms. Walsh — who is Mr. Jackson’s life partner — also produces his films and writes music for them. She has even directed scenes when Mr. Jackson was needed elsewhere.

“It’s impossible to overstate her importance,” said Andy Serkis, who returns as the craven creature Gollum in “The Hobbit: An Unexpected Journey,” which arrives in theaters on Dec. 14.

But Ms. Walsh, 53, is also one of Hollywood’s biggest living mysteries. She rarely grants interviews and refuses to sit for a photograph. Forget walking a red carpet alongside Mr. Jackson. Ms. Walsh has not even allowed her face to be shown on camera when contributing DVD commentary. She stayed home when Mr. Jackson visited the fan convention Comic-Con International in July.