He's clearly the evil man
When Duryodhana was born, Vidura advises Dhritarashtra to kill him as he was prophesied to destroy to the whole Kuru family
He then asks Pandavas to go to Varanasi, on the advise of his evil minister Kanika, where he knows Duryodhana will kill them.
He then watches the dice game and what injustice that follows it, silently.
He finally makes his allegiance to Duryodhana, very clear in the first shloka of the Geeta.
And if you look at it, we all have a potential Dhritarashtra within us. You can even call it the brain.
It has to choose between the right, that is our conscience or the wrong, which is our ego. The ego within all of us, is the Duryodhana.
But ultimately, it is the brain that allows it to.