Hydro-Man is a water-based super-villain that appeared in Ultimate Spider-Man vs. The Sinister 6.
When Spider-Man, Kid Arachnid, Iron Spider, and Scarlet Spider answer a distress signal at an abandoned mall in Queens, they find a vacuum-sealed room where Hydro-Man was being held. Hydro-Man claimed that Nick Fury was keeping him in this hideout for his own protection, and they decide to bring him to the Triskelion. However, when Iron Spider looked up Hydro-Man's criminal record and found out that he is a villain, Hydro-Man sheds his charade and attacks the group, causing Iron Spider to do an emergency landing in the Queens neighborhood where Aunt May resides. In order to combat Hydro-Man, Spider-Man, Kid Arachnid, Iron Spider, and Scarlet Spider had to use freeze webs until they ran out. As a final plan, Spider-Man had his fellow spiders throw their web cartridges into Hydro-Man, which caused the released webbing to absorb Hydro-Man. Back at the Triskelion, Spider-Man receives word that the jet carrying Hydro-Man back to his prison got intercepted. This causes Spider-Man to suspect that Doctor Octopus was behind it and now has a possible candidate for the Sinister Six. This was confirmed in "The New Sinister 6" Pt. 1 where Hydro-Man appears as a member of Doctor Octopus' Sinister Six. He is shown sporting a new outfit (similar to the second outfit from the comics). During the attack on the Triskelion, Cloak uses his abilities to send Hydro-Man to the middle of the Atlantic Ocean. Hydro-Man returns where he causes a tidal wave on the Triskelion and then forms a waterspout around it.