Mr. Jones is the owner of Manor Farm in George Orwell's novella Animal Farm. The story begins with this description of him:
Mr. Jones, of the Manor Farm, had locked the hen-houses for the night, but was too drunk to remember to shut the pop-holes. With the ring of light from his lantern dancing from side to side, he lurched across the yard, kicked off his boots at the back door, drew himself a last glass of beer from the barrel in the scullery, and made his way up to bed, where Mrs. Jones was already snoring
From this sentence we learn several key things about Jones's character. He is a drunkard and he is quite careless with his farm as well as his farm animals. These are the two key elements of his character which cause him to lose his farm when the animals rebel. We do not see him again until he comes back to try to take back his farm, an effort which is unsuccessful.
Virtually everything else we learn about him is told to us by the animals rather than the animals. Old Major reminds the animals of this:
Boxer, the very day that those great muscles of yours lose their power, Jones will sell you to the knacker, who will cut your throat and boil you down for the foxhounds. As for the dogs, when they grow old and toothless, Jones ties a brick round their necks and drowns them in the nearest pond.
The first time the animals harvest the farm's crops, we learn that they know more about harvesting efficiently "than Jones ever did." And when Jones comes back to fight for his farm, he shoots at Snowball and wounds the pig but does not kill him' Jones is a poor shot (perhaps because he was drinking).
In short, Mr. Jones represents everything the animals are willing to fight against, which is why "you don't want Jones to come back, do you?" is such an effective tool for all the pigs to use against the animals; Squealer in particular uses some version of this line. Jones is a cruel, careless drunkard who let his life and livelihood be taken from him because of those things.
In this symbolic story, Jones represents the Russian czar who ruled his country during World War I but could not manage to hold the country (farm) together after the war. He is eventually replaced with Stalin (Napoleon), of course.