fiction - How to prevent turning off the reader at first with a protagonist with unlikeable traits but that becomes better later on?

I have a story where the protagonist, who is a warrior meant to be the story's hero, has several unlikable traits. He is proud, kind of cold, has a hatred for the people of the enemy State (without exceptions, which makes him support war and sees no problem in killing soldiers), has a limited knowledge and isn't much prudent. Of course, he has several qualities too, but it's not relevant for the question.

In the course of the plot, many things happen which leads him to start changing and becoming a better person (including becoming the opposite of these flaws) since half the plot's progress and slowly until the end.

The problem is: how can I non-verbally tell the reader that he will become a more likeable person but that it will take kind of long until that happens, and preventing the reader from losing interest in the story until the change begins?

Answer

1. 
   

   You can foreshadow the change by showing the kernel of goodness that lies in the bad person. Options are "pet the dog" (the protagonist shows kindness to an animal, a child, an old person, etc.) or "save the cat" (the protagonist actively helps an animal, child, etc., often at risk to his own life).

   
   
   


2. 
   

   You can tell the reader. Many books begin with a sentence ("It was the last day of my life.") or prologue (see this question) that shows how the story will climax or end.

   
   


3. 
   

   Explain it on the blurb ("The story of a barbarian turning good.") or through the title ("Turning Good").

   
   


4. 
   

   Give him a likeable sidekick or co-protagonist. This doesn't have to be a humorous character but can be someone suffering under the protagonist who the readers sympathise with and root for.

   
   



5. 
   

   Make him "heroically bad", instead of simply unlikeable. The Ice Queen has fans, but the bad step-mother hasn't. That is give him great power and ability, and a great purpose.

   
   


6. 
   

   Let the reader know why he is cold and full of hate. Conan isn't a very likeable character, but we learn that witnessing the killing of his family as a child and his slavery made him into that brutal, cold killer.

   
   


7. 
   

   Narrate the story in a humorous tone. Humour provides relief from all kinds of otherwise aversive content (e.g. gruesome violence becomes funny in a cartoon).

   
   


8. 
   
   

   Aim his hate at aspects of the world or humanity that readers can sympathize with (e.g. he hates people because they are greedy, stupid, mindless etc.).

   
   


9. 
   

   Narrate him realistically. That is, he isn't really "good" or "bad", but a real person with the potential to behave in many different way, caught in circumstances that brings out his bad side. Later he learns how to better deal with the difficulties in his life and changes his environment so it allows him to show his good side.