Peso Penguin is the medical officer of the Octonauts. He is a kind-hearted penguin from a large family who likes to help any injured sea creature. He is very shy and gets scared easily by Kwazii's spooky stories, but he can be brave when there is someone who needs his help. He has a little brother named Pinto who thinks he is a real hero and Pinto has even been to visit him a few times at the Octopod.
Peso is often the first to show fear when a mission involves any kind of danger, but he has shown that he is very capable of pulling through even the most stressful situations.
He's a talented medic, often gaining the trust of injured or frightened sea creatures far easier than his crew mates due to his gentle personality, politness and he's able to bandage them up even quicker. And sometimes he gives the underwater creature a sticker.
Like Captain Barnacles, Peso also has love for a specific kind of instrument. For him, it's the Xylophone and he plays it rather well, in "The Octonauts and The Beluga Whales" he plays the same song as the Beluga Whale song. In the original UK version of the show, Peso has a very mild British accent and his brother Pinto has a much stronger one. In the US version of the show, they were both given more Hispanic accents instead.