Ed Deepneau (first appeared in Insomnia)

Edward Deepneau was the husband of Helen Deepneau, the father of Natalie Deepneau, and the distant cousin of Aaron Deepneau; he was also a neighbor of Ralph Roberts, and a research chemist at Hawking Industries. In 1993, he came under the control of the Crimson King after Atropos cut his thread, turning him into a "wild card." He later died attempting to crash a prop-plane into the Derry Civic Centre in order to kill Susan Day; Roberts intervened, however, to save the life of Patrick Danville, a child in attendance.

Ed Deepneau is mentioned in the following books:

The Dark Tower III: The Waste Lands (Aug 1991)

Aaron Deepneau, a cousin of Ed's, is a major player in the quest for the Dark Tower.

“Don’t hurry off, Jake. Now that you’re here, come on over to the counter and have a cup of coffee. Your eyes will widen with amazement as I cut Aaron Deepneau’s spavined old Kiev Defense to ribbons.”
- Book 1 / Part II / Chapter 13

The Dark Tower VII: The Dark Tower (Sep 2004)

Nancy Deepneau tells Roland that she had an Uncle Ed, but it is not the same one that Stephen King wrote about in Insomnia. Roland believes that King named the antagonist, Ed Deepneau, to get their attention.

“Because the story hinges on the Dark Tower,” Nancy said, “and because there’s a character in it named Ed Deepneau. He happens to be the villain of the piece.” The villain of the piece, Roland thought. No wonder her color rose. “Do you have anyone by that name in your family?” he asked her. “We did,” she said. “In Bangor, which is the town King is writing about when he writes about Derry, as he does in this book. The real Ed Deepneau died in 1947, the year King was born. He was a bookkeeper, as inoffensive as milk and cookies. The one in Insomnia is a lunatic who falls under the power of the Crimson King. He attempts to turn an airplane into a bomb and crash it into a building, killing thousands of people.”
- Part 3 / Chapter III / Section 11