http://en.wikipedia.org/wiki/The_Littlest_Hobo
All three productions centered around a stray German Shepherd who wanders from town to town, helping people in need. In the movie, the dog was tethered to a lamb for most of the story. Although the concept was similar to that of Lassie, the Littlest Hobo did not have an owner, and despite the attempts of many people to adopt him, he preferred to be on his own, and would head off by himself at the end of each episode. Never actually named on-screen, the dog is therefore often referred to by the name Hobo (though he was often given names by his multitudes of temporary owners). Although there were recurring actors in both series, the only constant was the dog. The littlest Hobo was a bit like the A-Team but a dog.
Best sentence ever, perhaps, that last one.
Him leaving town always made me emotional as a kid, even though I knew he'd "be back" in the next episode.