King Arthur is the kickbutt warrior and star of some very famous legends. His story and adventures have been told and retold over time. He is kind of the Michael Jordan of European warriors. Does the phrase "the knights of the round table" or the name "Guinevere" ring bells in your mind? Well, King Arthur was basically the first knight in shining armor, and Guinevere was his ladylove who betrayed him by falling in love with Sir Lancelot. King Arthur's legends are still alive and well.
Unlike Heracles, he never became immortal. But he did have trouble with the ladies (like Heracles), and he was the most famous warrior of his time (like Heracles). Also like Heracles, Arthur had lots of juicy adventures. We could also argue that Arthur did achieve a kind of immortality, because his stories continue to be told about him today.