Duke Thomas owes his current life to Batman, and he's ok with that. After being saved by Batman during one of the Joker's greatest schemes, he rededicated his life to protecting others when it seemed like Batman was dead, and the Robin's were gone.
So, he got together with like-minded kids and created the We Are Robin movement. A large group of those who believed that the Robin symbol was for any who would be willing to take up the cause and protect the streets. And that's exactly what they did. They even teamed up with the actual four previous Robins at one time.
Despite not being trained like the others, Duke has proven more than once he can fight with the best of them, and was more than willing to do his part to save the day.