The main writer of the story of Borderlands 2 is a guy named Anthony Burch, who has a sister named Ashley, who did the voice work of Tiny Tina.
Apparently in their free time the duo record and upload a web series called “Hey Ash, Whatcha Playin’”? The father of the siblings makes several appearances in the web series and it seems he has a cameo in Borderlands 2 as well.
When you reach Tiny Tina in the DLC, look around her bus, and you should see this mural painted on one of the walls. It depicts their father as he is drawn in the web series wearing an eye patch and riding a unicorn (the unicorn is another reference from “Hey Ash, Whatcha Playin’”).