The Mahabharata is a Smriti text. It was written as remembered. The Gita, a part of The Mahabharata, is a Shruti text. It was heard as spoken by Lord Krishna. Both the texts have a lot to teach us, qualities that one can imbibe in one’s personal conduct and perhaps, in one's life. Here is a list of ten characters and what we can learn from what was once remembered by Vyasa and what was once heard by Arjuna.
Krishna opens his mouth and shows the entire cosmos to Arjuna. Krishna tells Arjuna that Dharma is both rock-like (Dhar) and pliable like wax (Flowing). Dharma is not your institutional religion. It is your natural and binding duty. It is of ethical nature and you are born with it. A king’s dharma is to perform his kingly duties. Dharma holds the cosmos together. Krishna teaches us how to be dutiful in challenging times.
Duryodhana teaches us how blind swa-dharma (desires for your own Self) can lead you to "Adharma." Duryodhana's greed is wrong, his methods are wrong. He teaches us that blind pride and wrong actions have consequences and one must be careful and thoughtful about their actions and thoughts.