Like his father, Atlantis has a dark reddish-brown coat, but slightly lighter. He has a tan marking that goes around his cheeks and muzzle and down to his belly. His paws and ear tips have the same tan color, but his paws have darker red-brown sock tips. the rest of his ears are a soft salmon-pinkish orange hue, and his fur tuft has a dark reddish-brown stripe. He has light purple-pink eyes. His tail has several dark navy blue hues ranging from light to dark, and his fin and tail-skirt is a dark gray.
Even when he's an adult, Atlantis has a very puppy-like personality. He's very playful and kind to those who are kind to him- but is extremely wary around strangers. Once comfortable around someone, he's a huge ray of sunshine and playfulness, happy to help anyone out who needs it.
Atlantis is the younger brother of Coral, born when Coral was five months old. They lived happily under the water, until their parents were taken away by poachers. Their parents managed to hide them between large coral beds, and Coral kept herself and her little brother hidden until she thought it was safe to leave. Unfortunately for young Coral, she had a hard time holding onto her one month old brother when the current became way too strong, and the two became completely separated. Young Atlantis was found and raised by a pod of dolphins that heard him crying. There was a new mother in the pod who recently lost her child, and she helped raise Atlantis as her own, nursing him and helping him grow big and strong. He has vague memories of his sister, and hopes to some day find her and his parents again.
- named after the Lost city of Atlantis
- His best friend is a dolphin pup named Seaweed and is also extremely close to another merpup named Marine, she was the first merpup he met after being separated from his sister for so long and he took to her quickly.
- As a merpup, Atlantis has the ability to communicate with water critters when the pups on land cannot, making it helpful sometimes for the PAW Patrol to learn whereabouts of any sea life in distress
- He also finds another merpup named Sebastian and befriends him
- As pups, Marine and Atlantis felt weird if anyone mentioned them possibly becoming sweethearts, claiming it strange since they were best friends. But as they grew older, both started to develop feelings for each other as they grew more mature (slightly for Atlantis, but not much), and eventually they do end up falling head over tail in love
- He and Marine end up having four pups in the future, Whirlpool, Anchor, Kelpie, and Mystic . They also end up adopting Clader
- Atlantis feels horrible and sad for the Lost Merpups and vows to help them find homes since he knows how scary it was to be on his own at a young age
- As a pup- he's voiced by Elizabeth Daily- voice of Rudy Tabootie in Chalkzone