Duncan Idaho in Dune

Duncan Idaho

In the original Dune, Idaho is a minor character. He shows up only three times: once to introduce Stilgar, once to drunkenly spill the beans about Hawat's plan in front of Jessica, and one final time to rescue Paul and Jessica and bring them to Kynes. He then heroically sacrifices himself to save Paul and… that's it. His role is done.

But Idaho does make a return in future novels as a ghola (that's a clone that shouldn't have the memories of the original person but usually ends up retrieving them anyway). We'll try to keep this spoiler free:

• In Dune Messiah and Children of Dune, Idaho returns as a ghola and plays a major role in the story. 
• In God Emperor of Dune, Idaho—an Idaho ghola at any rate—is one of the protagonists alongside Paul's son, Leto Atreides II.
• By the time we hit Heretics of Dune, Idaho is arguably the most important character in the entire Dune series.

So, Duncan Idaho is a super important character in the Dune series as a whole, but his humble origins are that of a minor character in the original novel.