I got to year 2037 and still hadn't received the option of hiring Todd H, despite looking for him every month (this is when the list of staff members to hire gets refreshed).
On 15th October 2015, the developers released a statement on the Steam community forums
stating that Todd H. could be hired as the 46th employee. Having tested this, Todd H. was actually the 44th employee.
So, to unlock this achievement you'll need to hire 43 employees in order to hire Todd H. If he's not the 44th employee, just keep building Workstations and hiring employees - the maximum amount of employees you can hire is 50, so it may require you to hire all 50 employees in order to find him. If he doesn't show, just keep letting months pass where the list of staff members refresh.