Human nature and environmental factors can always contribute to the development of personality. Sadly, not everyone sees the opportunities presented by unfortunate events and rather than learn from them, they become consumed by them. Such is the case with Othello in Othello and Victor in Frankenstein.  

Othello is a respected and successful  commander in the Venetian army. He seems confident and assured and certainly did not "bewitch" Desdemona. He is glad to remind others that Desdemona

"had eyes and chose me" (III.iii.189).

It will only become apparent later that all his talk about Desdemona and how she was enthralled by his exploits is more to convince himself and in fact he subsequently doubts that she could really love him, becoming particularly sensitive to his position as an outsider - not a Venetian- and a Moor!

Othello is a passionate man but his passion is misdirected, as is his trust. Being aware of Iago's military position, he assumes that Iago must be an honorable man and blindly places all his trust in "honest, honest Iago." It seems inconceivable that he could trust Iago and not Desdemona but he views circumstantial evidence without considering its merits - and the damage is done.

Othello is something of a perfectionist and when he (thinks he)realizes that his marriage to Desdemona is not perfect, he acts without rational pause. Hence he kills not only Desdemona but himself.  He focuses on one thing at a time to the exclusion of all else and this is his downfall. The handkerchief becomes

damning physical evidence in his confrontation

and he does not even register Desdemona's protestations. It is all Othello's insecurities that collectively ensure his demise.

On the other hand, Victor in Frankenstein comes from a loving family who go beyond the call of duty in their attitude and love for others.  

Similarly with Othello, he is passionate and focuses on specific things, excluding all else. He is encouraged by others due to a recognition of his skills - much like Othello on the battlefield- and wants to leave a

 lasting impression on his fellow humanity.

Victor does not stop to think about the consequences of his actions. Othello only realizes after he has killed Desdemona that he was manipulated by Iago. Surely, he knew that killing someone would do more than supposedly save that person  from themselves and others:  

she must die, else she'll betray more men Vii(6)

He and Victor are thus alike in this respect as they had many opportunities to consider their actions and to make things right. Victor can only acknowledge that he owes the "creature" "a small portion of happiness."

Victor and Othello are so concerned with their obsession that they fail to recognize their own flaws. Othello wants to punish Desdemona but fails to see that he is therefore a far worse person. Victor is concerned about the creature's actions and behavior towards others but cannot see his own cruelty towards the creature.

Victor's actions contrast sharply to his family's and Othello's actions contrast sharply to Desdemona's who, even when she knows something terrible will happen, remains loyal to Othello.

The transformation of both characters to "monstrous" is gradual and complete.