Dhritarashtra, Pandu and Vidura were trained by Bhishma and Kripacharya in military arts and vedic knowledge.
Dhritarashtra, through a boon given by Veda Vyasa, had the strength of hundred elephants. He was able to crush iron with his bare hands but due to his disability, he was unable to use weapons.
Pandu was known as a Maharathi, being an excellent archer. While Vidura, though being the half-brother of Dhritarashtra and Pandu, had a low status, as he was the son of a handmaiden.
Bhisma taught Vidura about dharma, he learnt the dharmic rules and values, becoming the wisest of the three, because of which he became the Mahamantri (Prime Minister) of Hastinapur.
When it was time for choosing an heir for the throne, Vidura proposed that Dhritarashtra was the elder one but was a handicap, so Pandu should be chosen to succeed the throne. Thus, Pandu the next Kuru King of Hastinapur.