The Light Theory is an alternate theory regarding the purposes of the Slender Man.
The Light Theory explains that the Slender Man, and possibly other beings, is/are in pursuit of an object/being called the Light. It is not known what or who the Light exactly is, but references to it have been made by Choices. This in itself is strange because Choices was the one who said that the Aspect Theory was correct.
The Light Theory was built upon by Answered, and he thought that whoever found the Light had power to control the Slender Man, and/or any other beings who wished to control the Light. This too was confirmed by Choices. Due to the fact that we don't know what the Light is, this makes finding it rather difficult.
Eventually Answered became so obsessed with this Theory that he left everything in order to perfect it. He wanted to find the Light before anyone else did. Although at first his intention was to defeat the Slender Man, he may have changed goals before he was abducted.