The creature is someone who is in great pain, most especially because he has been isolated and alienated by human...
In Mary Shelley's Frankenstein, one of its major ironies is how the creature is often perceived as a monster, but how Victor rivals the creature for that label.
The creature is someone who is in great pain, most especially because he has been isolated and alienated by human beings. He feels very much alone. This is demonstrated as the creature describes his desperate attempt to connect with the De Lacey family:
I am an unfortunate and deserted creature; I look around, and I have no relation or friend upon earth. These amiable people to whom I go have never seen me, and know little of me. I am full of fears; for if I fail there, I am an outcast in the world for ever.
As the creature takes out his frustration and anger on Victor and his family, Victor also experiences alienation and isolation—family members are lost, and he has a secret that he cannot share: he is to blame for creating the monster; and who would believe him in the first place? Society might quickly lock him up, calling him insane.
Both the monster and Victor "play God." Victor creates life, and the creature takes life. The creature's anger first spills out on William Frankenstein, Victor's brother. The creature kills him to avenge himself against Victor:
‘Child, what is the meaning of this? I do not intend to hurt you; listen to me.’ “He struggled violently. ‘Let me go,’ he cried; ‘monster! ugly wretch! you wish to eat me, and tear me to pieces—You are an ogre—Let me go, or I will tell my papa.’
“ ‘Boy, you will never see your father again; you must come with me.’
“ ‘Hideous monster! let me go. My papa is a Syndic—he is M. Frankenstein— he will punish you. You dare not keep me.’
“ ‘Frankenstein! you belong then to my enemy—to him towards whom I have sworn eternal revenge; you shall be my first victim.’
Though Victor has been advised by those more knowledgeable, with a stronger sense of morality, he proceeds forward with his experiments without considering the fallout of creating life. First he discovers the secret that should not be in the hands of mankind:
After days and nights of incredible labour and fatigue, I succeeded in discovering the cause of generation and life; nay, more, I became myself capable of bestowing animation upon lifeless matter.
Then Victor creates new life in the monster and rather than assuming his responsibilities as a creator, abandons the creature and sets him loose upon mankind.
...now that I had finished, the beauty of the dream vanished, and breathless horror and disgust filled my heart. Unable to endure the aspect of the being I had created, I rushed out of the room, and continued a long time traversing my bedchamber, unable to compose my mind to sleep.
On a very basic level, other similarities they share are that Victor and the creature are both very intelligent, and each is capable of love and hatred.
While at first glance it seems that the creator and the creature are very different, Victor and his monster have more in common than one might first imagine.