"Book 'em, Danno."
If you know those three words, you know the vibe. You can probably already hear that legendary surf-rock drum roll and the brass section kicking in. But depending on when you grew up, the face that pops into your head when you think of Detective Danny Williams is going to be very different.
The question of who played Danno in Hawaii Five-O actually has two distinct answers that span fifty years of television history. It’s not just about a name on a casting sheet. It's about how two very different actors took a sidekick role and turned it into the emotional heartbeat of one of the most successful police procedurals ever made.
James MacArthur was the original. Scott Caan was the reboot.
They didn't just play the same guy; they defined two completely different eras of "cool" in the islands.
The Original Legend: James MacArthur’s Danno
Back in 1968, television was a different beast. Leonard Freeman, the creator of the original series, needed someone who could stand next to the towering, stoic presence of Jack Lord’s Steve McGarrett. He found that in James MacArthur.
MacArthur wasn't some random newcomer. He was Hollywood royalty, the adopted son of legendary actress Helen Hayes and playwright Charles MacArthur. Before he ever stepped foot on a Hawaiian set, he was already a Disney favorite, starring in films like Swiss Family Robinson.
He brought a certain polished, Ivy League competence to the role.
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In the original run, Danno was the dependable right hand. He was the one who followed orders, did the legwork, and stayed cool under pressure. While McGarrett was the granite-faced leader, MacArthur provided a softer, more relatable entry point for the audience. He played the character for eleven seasons—from 1968 to 1979—before finally deciding he’d had enough of the surf and sand.
Honestly, the show felt different after he left. For that final twelfth season, the chemistry was off. You realize pretty quickly when watching those old episodes that MacArthur’s understated performance was the glue holding the Five-O team together. He wasn't trying to outshine Jack Lord; he was making Jack Lord look better.
The Reboot Revolution: Scott Caan’s Interpretation
Fast forward to 2010. CBS decides to bring the show back.
The big worry? How do you replace an icon? You don't try to mimic him.
When people ask who played Danno in Hawaii Five-O in the modern era, they’re talking about Scott Caan. If MacArthur was the "reliable younger brother" type, Caan was the "grumpy, Jersey-born firecracker."
It was a stroke of casting genius.
Caan didn't play Danny Williams as a loyal soldier. He played him as a man who hated the beach, hated the heat, and spent half his time arguing with Alex O'Loughlin's McGarrett about "proper" police procedure. This birthed the famous "cargument"—those long scenes of the two leads bickering in a moving Chevy Camaro that became the staple of the reboot.
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Caan brought an edge. A nervous, high-strung energy that perfectly offset the new McGarrett’s Navy SEAL intensity. He also added a layer of fatherhood that wasn't as central in the original. His "Danno" nickname wasn't just a shorthand for Danny; it was a cute mispronunciation by his daughter, Grace, which gave the character a massive amount of heart.
Why the Casting Worked Twice
It’s rare for a reboot to last ten seasons. It’s even rarer for a reboot character to be as beloved as the original.
The secret was the chemistry.
James MacArthur and Jack Lord had a professional, respectful bond that mirrored the workplace culture of the late 60s. Scott Caan and Alex O'Loughlin had a "bromance" that felt like a modern, messy friendship. Caan’s performance earned him a Golden Globe nomination in 2011, something that rarely happens for actors on a standard procedural.
Surprising Facts About the Dannos
There are some weird bits of trivia most people miss. For instance, James MacArthur wasn't actually the first person to play the role. In the original 1968 pilot, the character was played by an actor named Tim O'Kelly.
Test audiences didn't like him.
They thought he looked too young. They didn't buy him as a high-ranking detective. So, the producers made the tough call to recast, brought in MacArthur, and the rest is history.
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On the flip side, Scott Caan almost didn't do the show because he wanted to stay in Los Angeles to be near his family and focus on writing. To accommodate him, the show often wrote scripts where Danno was "on the mainland" for a few episodes a season. It’s why you’ll notice Caan is missing from certain chunks of the later years.
The Physical Toll of the Islands
Playing a detective in Hawaii sounds like a dream job, right?
Not always.
MacArthur talked often about the grueling pace of filming in the 70s. The humidity was brutal on the gear and the actors. Caan had his own struggles, particularly with physical injuries. He’s a brown belt in Brazilian Jiu-Jitsu and very active, but the repetitive action scenes took a toll over a decade of filming.
How to Watch Them Today
If you’re looking to compare the two, you can find the original series on various classic TV streaming platforms like Paramount+ or via DVD sets that are still widely available. The reboot is a mainstay on Paramount+ and syndicated on channels like ION or TNT almost daily.
Watching an episode of the 1970s version followed by a 2010s version is like a time-capsule experiment. You see the evolution of Hawaii itself—from a sleepy tropical outpost to a bustling modern metropolis—mirrored in the way these two men played the same character.
What to Do Next
If you’re a fan of the "Danno" legacy, start by watching the Season 1 finale of the reboot, "Oia'i'o," to see Scott Caan at his most intense. Then, flip back to the original series episode "Retire in Sunny Hawaii—Forever" to see James MacArthur’s range (which actually guest-starred his mother, Helen Hayes).
To really appreciate the history, look for the 1997 failed pilot of Hawaii Five-O. It was an attempt to revive the series before the 2010 success, and it features James MacArthur returning as "Governor" Danny Williams. It’s a fascinating "what if" in television history that bridges the gap between the two iconic eras of the show.
Next Steps for Fans:
- Check out the 1997 pilot footage on YouTube to see James MacArthur’s final turn as the character.
- Compare the pilot episodes of both the 1968 and 2010 versions to see how the "Danno" introduction changed from a subordinate to a partner.
- Research James MacArthur's "James MacArthur Award for Excellence" if you're interested in the philanthropic legacy he left behind after his passing in 2010.