Spaghetti westerns had ceased to be serious stuff by the early 1970's, and people had started making comic westerns such as the Trinity series. Terence Hill was the new master of such movies, and when you combine him with the serious western star Henry Fonda, with some direction (not overall) by Sergei Leone, and with some great soundtrack by Ennio Morricone, you get a great movie. And this is what 'My Name is Nobody' was all about. Read more at this link:
The movie was mostly directed by Tonino Valerii, with Sergei Leone directing a few scenes, but since there was the involvement of Sergei, the movie came to be known as a Sergei Leone movie (something that Torino was not happy about). The music by Ennio Morricone was superb as usual.
However, 'My Name Is Nobody' is the story of a famous (and old) gunslinger Jack Beauregard (Henry Fonda); since he is famous, he is constantly hunted by the younger punks who want to challenge him, and if they win, they will be the next famous ones. Jack, after a lifetime of fighting, now just wants to hang up his boots, and is in Europe, hoping for some peace and quiet.