In Rock the Cradle he was first mentioned.
Becky was having trouble telling Jesse but told him. Later, in Happy Birthday Babies (Part 2), she has him and Nicky.
Jesse mixes up their booties by taking them off.
In D.J.'s Choice he learns to pump on a swing.
In Michelle Rides Again (Part 2), he takes Michelle's Red Rhino.
He was born to Jesse and Becky Katsopolis and grew up in the house with the Tanner family. 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 thier 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.
- Favorite animal: the 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 his brother Alex
- He was born on Michelle's fifth Birthday