AI Controller in Blueprint

We can create a Blueprint AI Controller by clicking on Add New | Blueprint Class | AI Controller. You will have to click All Classes and search for AI Controller to access it. You can see an example of this in the following screenshot:

For now, we will call our AI Controller BP_MyFirstAIController. Double-click on it to open the Blueprint Editor.

First, we need to create a variable so that we can store our Behavior Tree. Although it's not necessary to keep reference of the Behavior Tree, it's good practice to do so. To create a variable, we need to press the + Variable button in the My Blueprint panel, next to the Variables tab, as shown in the following screenshot (keep in mind that your cursor needs to be on the Variables tab for the button to show up):

Then, as a variable type, you need to select Behavior Tree and give it a name, such as BehaviorTreeReference. This is how what your variable should look like:

Then, in the Detail Panel, we will set the Default value (remember that to set the default value, the Blueprint needs to be compiled):

Then, we need to override the On Possess function, as shown in the following screenshot:

Finally, in the Event On Possess of the AI Controller, we need to start running/executing the Behavior Tree. We can achieve this by using the following simple node, named Run Behavior Tree:

As a result, your AI controller will be able to execute the Behavior Tree that's stored within the BehaviorTreeReference.