Elliot was born in Portland, Oregon, to Fred and Clara Elliot. Fred was of Scottish heritage; his grandparents were the first of his family to settle in North America. Clara's parents moved near the turn of the 20th century from Switzerland to eastern Washington, where they operated a large ranch. They met in Portland, where Clara was studying to be a chiropractor and Fred, having devoted himself to Christian ministry, was working as a traveling preacher with the Plymouth Brethren movement. Robert, their first child, was born in 1921 while they were living in Seattle, and he was followed by Herbert, Jim, and Jane, all three of whom were born after the family moved to Portland. Elliot's parents had firm Christian beliefs, and they raised their children accordingly, taking them to church and reading the Bible regularly. Elliot professed faith in Jesus at the age of six and grew up in a home where obedience and honesty were enforced. The Elliot parents encouraged their children to be adventurous, and encouraged them to "live for Christ".