As dayone mentions, Marriott has had a rewards program since the 80s, 1983 I think, was the start date. But Marriott Rewards, the current program, started in 1997 (or close to then).

Before that, each of Marriott's brands had their own separate programs (Marriott Marquis, Courtyard Club, etc.). Back in the 90s, I was staying a lot in the CYs and had lifetime Gold CY Club membership (the top CY level). That was great as it provided suite upgrades and free breakfast coupons (as well as free nights for every 12 nights stayed).