Finishing the Second Dream Quest in Warframe gives you access to your Operator. The game lets you design him or her:

This is how I designed my Operator:

You can read more about the Operator here: https://warframe.fandom.com/wiki/Operator.

My access to him is still very limited when playing missions, I can only use him through Transference, he'll be blasting a laser beam for 10 seconds. I need to play a lot to gather Focus points which will help me unlock new skills for my Operator. There's also another quest which would let me play as the Operator himself.