How is Frankenstein portrayed as the ultimate human?
I'm not sure that Victor Frankenstein is the "ultimate" human, but he certainly is an example of the greatness and the weaknesses humans are suceptible to. What was noble in Victor's nature? It might be the fact that he strove to advance medical science so that he might put an end to pain, suffering, and the distress that flesh is heir to. He used his intelligence to (re)create life and in doing so, became God-like in his innovation.
What wasn't noble in his nature? Victor became so obsessed with his own ends that he completely ignored those around him who loved and cherished him. He sacrificed love and relationships for his job and for success. Unfortunately, this is all too common for humanity. Victor also broke moral and ethical rules when he grave robbed and used parts of other dead people to make a living organism. Finally, Victor abandons his "son" because he was too scared or too weak to assume responsibility and be an ideal "father."
Victor is an ultimate human because he has ultimate potential and ultimate weaknesses inherent to us all.