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1. Is able to swim faster than competitive speed walkers.
Aquaman can swim 150 miles per hour (or 10,000 by some sources). Phelps has a top speed of just 4.7 miles per hour, which is merely a brisk walking pace.
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2. Lost advertising revenue after appearing in media with drug paraphernalia.
A British tabloid in 2009 posted a photo of Phelps using a bong. Advertisers have never criticized Aquaman for any alleged drug use... yet.
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3. Known to use the "dolphin kick" up to a range of 15 metres.
This is a competitive swim technique where someone swims under the water to reduce surface drag. Aquaman doesn't seem to do the dolphin kick.
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4. Has famously swum with computer-generated sharks.
For Shark Week, Phelps competed in a race against a CGI shark. Aquaman, of course, appeared in a movie with many CGI sharks.
Michael Phelps
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5. Named People Magazine's sexiest man of the year
Neither Phelps nor anyone who has played Aquaman has won the award. Jason Momoa was robbed in 2019.
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6. Has an abnormally long wingspan, proportionally longer than a typical... human... wingspan.
Phelps's wingspan is about 6'7" and he's only 6'4". It's unusual for people to have a wingspan longer than their height. Aquaman's wingspan appears typical in most depictions.
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7. Enjoyed viewership in the tens of millions.
Michael Phelps's greatest viewership for a single race was 32 million. At over $1 billion in revenue, Aquaman surely has accrued tens of millions of views.
Michael Phelps
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8. Taught an octopus how to milk a cow and took a bath in the milk.
Aquaman managed this feat in the comics. I have found no evidence of Phelps trying to help an octopus milk a cow.
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9. Is technically royalty.
Aquaman is the king of Atlantis. Phelps is from Baltimore.
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10. Found the Trident of Atlan, a sacred Atlantean relic who grants kingship to whomever possesses it.
Aquaman obtained this relic in his blockbuster movie. Phelps has failed to find any Atlantean relics; not everyone can be successful.
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11. Born in America.
Aquaman is from Atlantis. Phelps is from Baltimore.
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12. Started in 1985.
Phelps was born in 1985. Aquaman made his first appearance in 1941.
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13. Attended Prince William and Kate Middleton's wedding.
Phelps did not attend the wedding. There is no evidence that the royal pair would invite a B-list scrub superhero to their wedding.
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14. Is able to telepathically communicate with sea life.
There is no convincing evidence that Phelps can actually communicate with fish.
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Aquaman
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15. Is significantly more successful than anyone else in their realm.
Phelps has 56% more Olympic medals than the runner-up. Wow. Aquaman is probably only 5% the superhero that Superman is, but Superman typically stays out of the ocean because it's not his realm.
Michael Phelps
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16. Had an elaborate marriage ceremony with a fish bride.
Aquaman has only ever married Mera, who is an Atlantean, not a fish. Phelps has never married a fish.
Michael Phelps
Aquaman
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17. Suffers a susceptibility to dehydration when in arid or desert environments.
One of Aquaman's weaknesses is that he's at danger of dehydration when in the desert... much like all humans.
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18. His name was dropped in the #1 hit song "One Week" by Barenaked Ladies.
"You'll think you're looking at Aquaman; I summon fish to the dish, though I like the Chalet Swiss..."
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19. Married one "Miss California".
Aquaman has only ever married Mera whereas Phelps married a woman who won the Miss California pageant.
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20. His name appears in Barack Obama's book, "A Promised Land".
In response to being criticized about his response to the Deepwater Horizon oil spill, Obama claimed to have said, "What does he think I'm supposed to do? Put on my f------g Aquaman gear and swim down there myself with a wrench?"