( the D in the beginning of this name is pronounced like 'th' in 'brother'. The SH is pronounced like one between 's' in 'sum' and 'sh' in 'shut'.)
If ever a minor role had completely changed the entire course of the big plot, Daasha could be the best example.
Daasha was the chief of a fisherman class on the banks of river Yamuna. He was the foster father of Satyavathi, daughter of a king named Vasu. when Shanthanu asked for her daughter in marriage, he insisted that her own son should be the successor to the throne. That conditin lead to all that happened later.
Though a minor character, his role was of high importance.
Many arguments about the rights of Paandavas and Kouravas to the kingdom find their roots in the point raised by Daasha that Bheeshma's sons might come in the way even though Bheeshma himself relinquished his own right.