When the benefits adviser Ted Benna first thought up a new type of employee savings plan in 1980, the client he created it for rejected the idea as too risky. After all, no one had previously used the unremarkable section of the tax code called 401(k) to defer paying taxes on money that rank-and-file workers set aside for retirement.

So Mr. Benna decided to try it out at his own workplace, Johnson Companies, a small consulting firm outside Philadelphia.

Without intending to, Mr. Benna set off a revolution. Nearly 40 years later, 401(k) accounts are the most common employer-sponsored retirement plans and a raft on which millions of Americans hope to float through retirement.

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