What was the name of the dog in the RCA Victor trademark?

The dog's name was Little Nipper.

Surely Nipper was the name of the dog that was in the logo of the HMV records. Did RCA Victor steal him?

I think RCA Victor was the company and 'His Master's Voice' was the slogan. Later, they changed the company name to His Master's Voice and later still to HMV. It still operates as HMV.

The story about the dog was made up as a marketing stunt. It never really happened. Somebody painted a picture of a dog and made up a story and a slogan to go with it. In the story, the dog was certainly called Nipper or Little Nipper, I'm not sure which.

Gramophone was the original name of the company which bought Francis Barraud's painting titled "His Master's Voice." Here are two sites with a lot of information about Nipper.

https://en.wikipedia.org/wiki/Nipper

http://americacomesalive.com/2013/07/14/the-rca-dog-an-american-icon/

The dog's name is Nipper because he used to bite every boots and shoes ankle. The artist introduced it to the Royal Academy but rejected in contempt then he tried to sell it to gramophone manufacturers until he reached Emil Berliner's Gramophone Company, the gramophone and the record inventor, who bought the picture with the condition that the terrier would be clearly seen to be listening to Berliner's gramophone. That was in 1900 in 1924 the company was sold to Victor later RCA Victor. RCA fought in court on the right to use the dog as a trademark.