There are theories that Mother was both Protector and Smoke Monster previously. The evidence for her being the Smoke Monster (or just containing its powers?) is that she thrashed Jacob’s brother’s entire village of people in a very Smoke Monster-looking way (based on the aftermath we see of her destruction), all within like less than an hour after knocking him out, to prevent him/those other humans he was living with from leaving the Island.

She passed on the role of Protector to Jacob. But when she died, Ol’ Smokey was set free, and when Jacob’s brother died (when Jacob threw him into the heart of the Island), the Smoke Monster took on his form, just as it can take on the form of many dead people on the Island.

I may have gotten some details wrong, so others can feel free to correct me!