Here is the full list of all 11 One Sole Purpose achievements.
Successfully completed the tutorial
Completed Chapter 1 and made a new friend...at least you hope he is a friend
Defeated the protector and destroyed the sector
Protector of red is dead
Destroyed the "unstoppable" sentinel
Destroyed the final reactor core in the city of Azureus and assassinated the protector
Completed Chapter 2 and got some more energy in the process from a new guardian!
O captain! My dead captain!
.....
You are now the strongest guardian in existence!
Thanks for playing!