People often stopped them and asked to take photos.
"She's a hit on the streets of Portland," King said. "Very rarely do you see a cat riding on the top of someone's backpack."
King and his foster father, Walter Ebert, recently took the cat to a veterinarian in Helena, where a scan found a microchip, and the vet was able to contact Buss.
Buss is planning a party marking Mata's return, and King agrees it's an occasion for celebration.
But it's going to be emotional for King, too.
"I didn't want a cat in the first place. I just thought I was saving someone's cat," King said. "And that's what I've done. Now I've grown attached to her.
"My pack will be 20 pounds lighter," he said, "but a big hole, a big hole."