Nicholas "Nicky" Katsopolis (played by Daniel Renteria (season 5) and Blake Tuomy-Wilhoit (seasons 6–8); born November 12, 1991) is a fictional character on Full House. He is the son of Jesse and Rebecca Katsopolis and identical twin brother of Alex.
He was born to Jesse and Becky Katsopolis, who named him after Jesse's father Nick Katsopolis. Becky got pregnant with Nicky and his twin brother Alex and had trouble breaking the news to Jesse. She tries to tell him in a candlelight dinner but Jesse was too happy to go on tour. Later she told him in a game of Pictionary. On Michelle's birthday they had the twins. In Nicky and/or Alexander, Jesse mixes them up by taking off their booties and put Alex's booties on Nicky. Later he inks Alex's foot. Then Becky finds out.
Nicky, much like Alex, is a humorous and mischievous character. Throughout the seventh and eighth seasons, they caused trouble worth more than the two of them combined, let alone singular. They adore each other, which caused them to cling on each other until Jesse and Becky had them find their own personalities. They also were the focus of Jesse's attention and he tried to raise them the way that his own father never had, but it usually led to them overpowering him until Becky comes in with her motherly advice to him. Nevertheless, they are both still mischievous and cause much stress to their parents' lives.
- Rebecca Katsopolis (mother)
- Jesse Katsopolis (father)
- Alex Katsopolis (brother)
- Danny Tanner (uncle)
- Pamela Tanner (aunt; deceased)
- D.J. Tanner (cousin)
- Stephanie Tanner (cousin)
- Michelle Tanner (cousin)
- Irene Katsopolis (paternal grandmother)
- Nicolas Katsopolis (paternal grandfather)
- Nedra Donaldson (maternal grandmother)
- Iorgos Katsopolis (great-grandfather)
- Gina Katsopolis (great-grandmother)
- Jackson Fuller (first cousin, once removed)
- Max Fuller (first cousin, once removed)
- Tommy Fuller Jr. (first cousin, once removed)
- Tommy Fuller, Sr. (cousin-in-law; deceased)
- Teri Tanner (step-aunt)
- Favorite animal: lion
- Likes the color blue
- In "Stephanie's Wild Ride", it is revealed that his favorite story is "Three Billy Goats Gruff"
- He only likes to play with Alex
- He and Alex were born on Michelle's fifth birthday
After Full House ended he (and Alex) graduated from high school. In Fuller House Nicky and Alex are in college, they are planning to open up a fish taco truck business together, and they move back in with Jesse and Becky.