Mammoth Mutt
From superman.nu: Supermanica
Mammoth Mutt
The heroic alien dog with the ability to increase his size to a gigantic degree. Mammoth Mutt is a member of the Space Canine Patrol Agents, an interstellar group of canine secret agents of which Krypto is also a member (SB No. 131/3, Jul 1966: "The Dog from S.C.P.A!"; and others).