|First Episode||Past Tense|
|Voiced By||T. Ryder Smith|
|Alliances||the Original Team Venture|
Otto Aquarius (also known as the "Lost Son of Atlantis") is a half-Atlantean and a former member of the original Team Venture and was one of Jonas Venture Sr.'s close friends and allies. Otto, unlike his more questionable teammates, is actually a kind individual who prefers peaceful solutions over violence.
According to The Action Man, Otto was conceived when a drunken sailor impregnated his "mer-mom", although whether this is true or The Action Man was just being rude remains uncertain. At an unknown point, he became friends with Jonas Venture Sr. and joined Team Venture. He would take part in multiple adventures where he would aid his team by infiltrating villainous headquarters via waterways and then acting as a distraction to keep the villains busy. Otto continued to serve with Team Venture for many years but unlike his fellow teammates he never took part in any of the torment that they inflicted on Rusty.
He later retired along with the rest of the team after Jonas died from an unknown cause and Otto would spend his retirement as an active Jehovah's Witness going door to door spreading the word of his faith.
Otto Aquarius along with the rest of the original Team Venture was summoned by Hank and Dean Venture to save the kidnapped Rusty Venture from the mad scientist Mike Sorayama. In the end Rusty and Brock managed to escape by themselves, but Brock in a blind rage beat the daylights out of the original Team Venture. Luckily Otto and the others managed to survive with only a few injuries and broken bones.
Otto alongside the original Team Venture appeared on Spider-Skull Island during the opening of the Venture Museum.
Otto unlike his peers is actually a very kind and considerate individual and even when he was an active member of Team Venture, he was never seen engaging in violent acts, usually acting as a spy, infiltrator or diversion for the team. After his retirement, he became an active Jehovah's witness and a strict pacifist who refused to get involved in violent situations and appears to hyperventilate when exposed to them. He leads a group of young witnesses which he appears to care about dearly and unlike the other members of Team Venture it appears that he never showed signs of being antagonistic to Rusty and seems to be the most level-headed of his team alongside Paul Entmann, having never shown any unnecessarily hostile or arrogant behavior.
Otto has the ability to breath underwater and can telepathically communicate with sea life due to his Atlantean heritage. He is also a very capable swimmer. It appears that his main skill among Team Venture was infiltration and diversion. His Atlantean heritage also grants him a longer lifespan as shown with the fact that he still looks young and healthy in comparison to his teammates who have become old and frail.
- Otto Aquarius is an obvious reference to Namor the Sub Mariner and Aquaman, as shown by his Atlantean heritage, ability to communicate with fish and their similar backgrounds.