Nicholas "Nicky" Katsopolis II (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 the identical twin brother of Alex. In Fuller House, he becomes an adoptive brother to Pamela.
He was born to Jesse and Becky Katsopolis, who named him after Jesse's father Nick Katsopolis whom gave him great hair and raised him. 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. He is blonde, has blue eyes, and wears blue pajamas (as Michelle knew and Stephanie didn't in "The Perfect Couple").
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. His full name is Nicholas Katsopolis (which was addressed only once in "The Perfect Couple").
- Jesse Katsopolis (father)
- Rebecca Katsopolis (mother)
- Alex Katsopolis (brother)
- Connie Anderson (aunt)
- Corky Donaldson (uncle)
- Three unnamed uncles
- Danny Tanner (uncle)
- Pamela Tanner (aunt; deceased)
- D.J. Tanner (cousin)
- Stephanie Tanner (cousin)
- Michelle Tanner (cousin)
- Howie Anderson (cousin)
- Dick Donaldson (first cousin; once removed)
- Donna Donaldson (first cousin; once removed)
- Debbie Donaldson (second cousin)
- Darla Donaldson (second cousin)
- Irene Katsopolis (paternal grandmother)
- Nick Katsopolis (paternal grandfather)
- Nedra Donaldson (maternal grandmother)
- Kenneth Donaldson (maternal grandfather)
- Iorgos Katsopolis (great-grandfather; deceased)
- Gina Katsopolis (great-grandmother)
- Pamela Katsopolis (adoptive sister)
- 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)
- Unnamed first cousin; once removed (Stephanie's daughter)
- Favorite animal: lion
- Nicknames: Nick, Nickster
- 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
- Was born on Michelle's fifth birthday
- Is right-handed
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. Nicky and Alex eventually become big brothers after Jesse and Becky adopt a baby girl.