Text formatting question (strikethrough)

How can I format text so that it is struckthrough (strike) and can easily have the formatting removed (as in, the ability to easily toggle the strikethrough on the text)?

As in I have a text displaying a task and I have finished the task, so I click a button and the text has a strikethrough. But I would also like the ability to hit a button and remove the strikethrough formatting. What would be the best way to implement this?