Business Problem:

As a Sales/Account Manager, I need visibility on an Account to the Last Task Completed

Solution:  

Create a Text rollup of the most recent task completed.

  1. Create a Text field on Account (Most Recent Task Completed)
  2. Create a Text rollup of the most recent task and add a filter.
    1. Rollup Step 1:  Navigate to Rollup Helper and select Account
    2. Rollup Step 2:  Select the field you created (Most Recent Task Completed)
    3. Select Account Child - Task and select Subject as the field.  Select Text 
    4. Create a new filter:  
      1.  Limit Return to 1 Record
      2. Sort by Last Modified Date in Descending Order
      3. Specify Filter Criteria, Status =  Completed
  3. Save the filter, then Save and Run the rollup.