At some point, you might be in a situation, where you have a task assigned to a group of users and you want to know which user completed the task. There is a possibility to store the user who completed the task although it was originally assigned to a group of users. This could be quite useful for further executing the workflow, as you have another task which needs to be assigned to exactly that user for example.
You first need a field where you want to store the user in. It does not have to be a workflow variable it can also be a business entity field. In this example, a workflow variable is used. If you do not already have a variable to store the user, then you first need to create a workflow variable or add a business entity field.
Next, go to the task which has the group of users assigned and where you want to retrieve the performing user. Right-click it and choose Select business entity fields. There you have to select the variable you previously created or added. Hit OK. Right-click the task again but this time you choose Select user in charge.
In the Dynamic tab you have to select User name from the User properties list, and your variable from the Business entity field list. Now you only have to tick off both checkboxes and save the changes with clicking OK.