Well, I assume that you mean the classic cartoon 'Tom and Jerry' where a cat chased but is ultimately outwitted by a clever mouse. The dog in this cartoon is called 'Spike' and is an English bulldog. Spike is friendly to Jerry the mouse but not so keen on cats. Spike the bulldog first appears in a short cartoon 'Dog Trouble' (1942).
Spike is also sometimes referred to as Butch or Killer. In the 1949 cartoon 'Love that Pup' a new character, Tyke, Spike's son was introduced. He often got caught up in Tom and Jerry's disputes causing Spike to get involved. Spike and Tyke were mildly successful as a spin off in their own cartoons and comics. Spike's voice was modeled on that of Comedian Jimmy Durante particularly when he said to Tyke 'that's my boy.' Another, unrelated 'Spike the Bulldog' appears in the Looney Tunes and Merrie Melodies series by Warner Brothers with a bouncy sidekick called Chester the terrier.
Spike is also sometimes referred to as Butch or Killer. In the 1949 cartoon 'Love that Pup' a new character, Tyke, Spike's son was introduced. He often got caught up in Tom and Jerry's disputes causing Spike to get involved. Spike and Tyke were mildly successful as a spin off in their own cartoons and comics. Spike's voice was modeled on that of Comedian Jimmy Durante particularly when he said to Tyke 'that's my boy.' Another, unrelated 'Spike the Bulldog' appears in the Looney Tunes and Merrie Melodies series by Warner Brothers with a bouncy sidekick called Chester the terrier.