Cosmo is the pet dog in Fuller House.
Cosmo is born in the Tanner's backyard by D.J. Tanner-Fuller.
Max picks Cosmo out of the litter of puppies, and introduces him to the family as Cosmo T.D. Fuller.
Max practices for his school recital in front of Cosmo who is wearing a pair of Max's underpants.
Max is toilet training Cosmo, getting him to go outside or use a potty. When the power goes out Max sits with Cosmo in the dark in the living room thinking it could be the zombie apocalypse. After Ramona's party Max and Cosmo see Kimmy and Fernando kiss from Cosmo's dog house.
Cosmo chews up the couch. When Max tries to get Cosmo to do tricks for his friends he just lies down.
After 1,000 roses show up, Cosmo takes off with the card that has the senders name on it, and no one notices. Cosmo has been hoarding items under Max's bed.
Max tries to teach Cosmo and Tommy tricks by feeding them both dog food.
Max hides out in the dog house with Cosmo.Jesse and Becky renew their vows and Kimmy and Fernando almost get remarried.
Max shows Stephanie and Kimmy that he taught Cosmo how to roll over during the summer.
After Max brings Cosmo back inside from doing his business in the yard, Fernando gives a piece of his bacon wrapped bacon flavoured bacon on a bed on bacon appetisers to Cosmo to eat. Max gets Cosmo to lick his face then Max wipes his hand down his cheek and smells the bacon flavour.
Max lets Cosmo know that when he kisses him it means that he loves him. While Max is in his room tickling Tommy and Cosmo on his bed there is a knock at the window, it's Ramona wanting to hide from her parents.
It's Halloween and Cosmo is dressed in a red cape and horns for Max's spooky party.
After Max gets chicken for his "One Kid Can Make a Difference" project, Max throws Cosmo a corn cob to fetch and he swallows it whole. Because dogs can't digest food that large, D.J., Max, Jackson and Matt take him to the Pet Clinic. Matt gets a x-ray of Cosmo to see exactly where the corn cob is located. D.J. and Matt operate on Cosmo to remove the corn cob.
After the operation Max comes in he tells D.J. he doesn't deserve to be Cosmo's Doggy Daddy anymore and she should look after him. D.J. tells Max he did what he did out of love and Max gives himself a second chance. Matt lift's Max up so he can give Cosmo a kiss.
Max, D.J., Jackson and Cosmo arrive home and Max wants to celebrate Cosmo being alright by having chocolate ice cream, D.J. lets Max know chocolate is poisonous for dogs.
It's Thanksgiving and it's going to be a very full house. While D.J. and Matt prepare Thanksgiving dinner, Danny, Jesse, Joey, Stephanie, Becky, Kimmy, Jackson, Ramona, Max, Tommy, Fernando, Jimmy, Nicky, Alex, Ginger, Phyllis, Jerry, Joan, Lewis and Cosmo are out playing football. By the time everyone arrives home they're 90 minutes late for the family photo. D.J. tries to take the family photo in the living room but no one will stay still.
Max takes Cosmo outside to find that all his crops have grown back overnight.
Jackson lets Cosmo know that his girlfriend Lola is bringing her new dog Spot over to spend the night, so play nice be careful where to sniff.
After finding out Jimmy's music video for Stephanie's song isn't doing well, Kimmy gets the idea to pander to the lowest common denominator and use Tommy and Cosmo in the video instead.
D.J. watches as Matt comforts Jackson and Max while they're sick and brings Tommy and Cosmo into the bed with them.
It's D.J.'s 39th birthday and New Kids on the Block (NKOTB) are at the house. NKOTB recognise Tommy and Cosmo from the music video Jimmy created and get Stephanie to take a photo.
Jackson lies on his bed with Cosmo.
It's December 23rd and Kimmy arrives home early with D.J. as Jimmy and Stephanie are trying to take a surprise family Christmas photo for her of Jackson, Max, Tommy, and Cosmo with Fernando dressed as Santa. Steve, CJ and Rose arrive with an after-hour sick pet situation. Rose's pet bunny rabbit Jack won't eat so D.J. decides to keep an eye on him overnight. Cosmo has an instant attraction to Jack.
Christmas Day. Cosmo brings Jack a carrot not knowing that Jack like Cosmo is also a male.
It's the first day of summer and Tommy appears in Max's musical dream about having the 'Best Summer Ever' with Cosmo.
Cosmo lays in the sun on a fold-out chair wearing shades and shorts at Max's pool party.
It's the 4th of July and Cosmo wins "Danny Tanner's World's cleanest pie eating contest", just like his great grandfather Comet did back in 1991. Danny gives Cosmo the Golden Napkin trophy.
Mankowski believes he can understand dogs and that Cosmo has told him that his real name is Derrick. Cosmo respond to Derrick when he is called.
Cosmo comes inside covered in mud, and follows Jackson, Max and Jesse as they chase each other around the kitchen.
Max is having an existential crisis after Tommy destroys his beloved Uni so he sits with his emotional support animal Cosmo.
Jackson announces for everyone to do less lovey-dovey family stuff and specifically tells Tommy and Cosmo not do do anything ridiculously cute. Tommy kisses Cosmo then Cosmo licks Tommy and Tommy puts his arm around Cosmo.
When Max let's Cosmo outside, Max hands Cosmo a bag to collect his own business in.
Tommy plays doctor with Cosmo.
Stephanie reads to Cosmo thinking it's Max after Max puts Cosmo in his bed wearing a wig and his pyjamas.
Just after Rocki announces that she believes the Fuller's live in an artificial world of sugar-coated sweetness, Tommy and Cosmo walk through the kitchen in matching sunglasses and bandanna's around their necks.
When Max acts as the ancient mariner statute head in an attempt to fool everyone, Cosmo doesn't fall for the trick and starts barking at him.
Fernando races Tommy and Cosmo around the living room.the Smash Club along with Danny, Jesse, Joey, D.J., Stephanie, Becky, Kimmy, Fernando, Jackson, Ramona, Max, Tommy, Steve, Jimmy, Rose, Pamela, Rocki, Vicki and the Rippers.
Cosmo watches Die Hard with Jackson, Ramona, Fernando and Jimmy. Later D.J. tries to help put Max back in the Christmas spirit she puts on a "Fuller Family Holiday Extravaganza" where Cosmo wears antlers and a red nose.
Cosmo wears Jackson's pants in an effort in make them look played in but they are still too clean so Max orders him to try the puddle in the backyard.
D.J., Stephanie, Kimmy, Jackson, Ramona, Max, Tommy, Fernando, Steve, Jimmy, Pamela and Cosmo are in attendance at the gender reveal party when Jesse arrives with Ben. Cosmo eats Max's sandwich off a plate that Max left on the ground.Bayview High School gym before the prom. Cosmo didn't sniff out any contraband but he did get into the donuts and is riding a wicked sugar high. Cosmo got the last maple bar now he and Steve aren't speaking.
Steve has planned a girls vs guys Amazing Race themed game called "D.J.'s Amazing Race: Birthday Edition" for D.J.'s 40th birthday. Steve has set up D.J.'s party in the back yard, including a stage. Steve gathers everyone around. Steve wanted to make D.J.'s 40th birthday a really special day and give her something that she'd always remember. He pulls a draw-string to make the curtain fall from in front of the stage to reveal "Your Kids on the Block". Jackson, Ramona, Max, Tommy, and Cosmo are on the stage. They dance and lip-sync to Fool me Once.
Jackson admits to D.J. that Cosmo messed up on the choreography because he only showed up to half the rehearsals.
While Kimmy is getting her hair done, D.J. shows Fernando her over-the-top proposal idea. D.J. introduces the fearless lion tamer, Tommy, and his ferocious beast, Cosmo. Cosmo wears a lion mane.
When Let's Get Married starts playing a flash mob emerges on the street. D.J., Stephanie, Jackson, Ramona, Max, Tommy, Fernando, Jimmy, Cosmo, Matt, Rocki, Ethan are joined by back-up dances for the big proposal. Fernando removes Kimmy's cast and she gets up and starts dancing. D.J. is confused, this is not what they practised. Jesse and Joey tango up to D.J. together. Danny tells D.J. he had to be there for her big moment. With D.J. still confused, the dancing stops and Jesse plays soft music on his guitar. Steve comes walking through the crowd and asks Danny for his blessing. Steve get's down on one knee in front of everyone and proposes. To which D.J. responds "Yes. Yes. A million times yes".
It's Thanksgiving day. Cosmo runs in with green bean casserole all over his head.
- In the episode Nutcrackers, Cosmo was voiced by Dave Coulier.
- On December 16, 2019 it was announced that Cosmo (which is also the dogs real name) had sadly passed away from surgery complications.