What is "we-chank-wash-ta-don-pee"

We-Chank-Wash-ta-don-pee, or Chaska (pronounced chas-KAY) (died December 26, 1862) was a Native American of the Dakota who was executed in a mass hanging near Mankato, Minnesota in the wake of the Dakota War of 1862, despite the fact that President Abraham Lincoln had commuted his death sentence days earlier.