He is an old Basset Hound. He has white fur with light brown spots and dark brown spots. He also uses a blue wheelchair.
Pops genuinely appears to be a grumpy old Basset Hound who hardly ever seems to be happy. He genuinely rushes the pets through the city with little to no regard for them. However, he does appear to be caring, as he did help Gidget track down Max and Duke. It is possible that due to his old age, he may actually be delusional, as he viewed Chloe (or "Rhonda") as his girlfriend and he ignores all her attempts to convince him otherwise. He also seems to find Max and Gidget's romance to be disgusting.
Pops lives in a big apartment and his owner is often away. Thus, his apertment always has big parties held by dozens of pets. Before Buddy finds him, he is having a massage by a hamster. Buddy calls him by but he doesn't hear at first, but when he calls louder, another hamster with a fan accidentally hits Pops and he falls from some cushions and Pops identifies Buddy. Buddy greets Pops and Pops replies that he has been paralyzed; Gidget asks Pops about Max, who is last heard from in the sewer.
Pops says he does know someone (Snowball) in the sewer but he hasn't been there for a long time. Chloe then mutters that they're wasting time and asks if Pops has seen himself because his eyes are closed. So Pops askes Myron to open his eyelid so he can take a look see at Chloe. Eventually Pops agrees to help Gidget and he evacuates all pets by having Myron operate a vacuum.
Pops goes to the sewer through a long route. He and the pets go by a cherry picker, a flock of pigeons, the apartment of the man who lost Max and Duke earlier, construction tools, and lastly a big slide in a construction site. He and the pets soon finds out Snowball wants to catch Max so they escape before The Flushed Pets reach them. They continue to look for Max and finally saves him from being attacked by The Flushed Pets on Brooklyn Bridge. With the help of Tattoo who's driving a taxi, he goes home before his owner is back.
The Secret Life of Pets