Help please, my hamster is strangely aggressive

[MrGorbachev]

I have a dwarf hamster (Russian) I’ve had him for a little over a week now, and he’s just so aggressive. When I put my hand in his cage, he runs at it to bite at it and I don’t think it’s cage aggression because he’s in a 20 gallon long... he has plenty of room and a wheel. I want to start taking him, but I can’t because every time I put my hand in to give him a treat or to let him sniff, he’s more interested in going at me to bite. He even bites the toilet paper I put in his cage that smells like me. I’m so sad because I just want him to like me. Please help me.

[mangoandmimi]

It does sound like he could be territorial - I wouldn't call it aggression, often when you take them out of the cage they're perfectly fine. And the size of the cage doesn't always make a difference. Generally with cases like that you just have to take taming at a slower pace and it may help to take him out of the cage to tame him. I'd also make sure you've washed your hands preferably with unscented soap before you go near him or do anything with the cage.
A 20 gallon long isn't big enough long term IMO a 40 gallon breeder or larger would be a better size. I'm wondering what the cage looks like if you have a setup photo, as if he doesn't feel settled or doesn't have enough places to hide it can also lead to this kind of behaviour.

Although I have to say with some of my previously territorial hams I've still done a lot of the taming in the cage and just put up with the biting! I do like in-cage taming, it gives them the choice to come up to you and everything is done at their pace. As long as it doesn't draw blood (dwarfs don't a lot of the time) it's generally bearable and they've slowly improved with time and patience.