Alexander "Alex" Katsopolis (born November 1, 1991) is a fictional character on Full House (played by Kevin Renteria: season 5 and Dylan Tuomy-Wilhoit: seasons 6–8). He is the son of Jesse and Rebecca Katsopolis and identical twin brother of Nicky. In Fuller House, he becomes an adoptive brother to Pamela.
He grew up in the house with the Tanner family. Becky got pregnant with Alex and his twin brother Nicky 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 was named after Becky's teacher who gave her the inspiration to study journalism. He is blonde, has blue eyes, and wears red pajamas (as Michelle knew and Stephanie didn't in "The Perfect Couple").
Alex, much like Nicky, 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(Support Your Local Parents)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 for him. Nevertheless, they are both still mischievous and cause much stress to their parents' lives.
- Rebecca Katsopolis (mother)
- Jesse Katsopolis (father)
- Nicky 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)
- Danielle Gibbler (first cousin; once removed)
- Favorite animal: lion
- Nickname: Big Al
- Alex's favorite color is red.
- He sleeps in a red race car bed.
- In "Stephanie's Wild Ride", it is revealed that his favorite story is "Three Billy Goats Gruff".
- He and Nicky were born on Michelle's fifth birthday.
- Alex was named after Becky's favorite college professor who inspired her to go into journalism.
- Alex and Nicky were born on November 1, 1991. It is unknown who was born first.
After Full House ended, he (and Nicky) graduated from high school. In Fuller House Nicky and Alex are in college, and open up a fish taco truck business together, after moving back in with Jesse and Becky. Nicky and Alex eventually become big brothers after Jesse and Becky adopt a baby girl. Nicky and Alex join their parents and Danny when they move to Los Angeles.