Every day Hachikō waited for the professor at the Shibuya Station. In May 1925, Professor Ueno had a stroke while lecturing and died. Hachikō was given to a new family but fled back to his old home, searching for his friend. When he did not find him there, he waited at the at the train station.
Hachikō continued to wait. Every day, until his death in 1935, the dog waited patiently for his friend to return. More of his story can be found on Wikipedia.
In 2009 Richard Gere starred in a film about Hachikō, but I’m partial to this little gem.