Struggling with my nervous roborovski hamster

[Lillie16]

Hi everyone, I am new here and just looking for some advice
I have two hamsters, I have had my Russian dwarf hamster for about a year and a half and tamed her easily and have no problems with her, she is a lovely natured and loving hamster. However, I adopted my other hamster, a roborovski hamster, about 8 months ago from a girl I know who did not want him after 2 months of getting him. She gave him up to us as he was very nervous, constantly running on his wheel and being aggressive and biting. Since adopting him I have tried my best to tame him and have spent lots of time over these past 8 months giving him treats and putting my hand into his cage (whilst wearing gloves as he is a biter). However despite all my efforts to tame him nothing seems to be working and he is still aggressive, extremely anxious and always runs in his wheel when he seems frightened! Please could anyone give me any advice on taming him and making him less frightened? My other hamster absolutely loves being out of her cage and having cuddles and I find it a shame that my other hamster doesn’t get this.
Thankyou