Aside from dissolve, this can be also be done dynamically in an Edit Session.
You start by selecting the features you want 'dissolved'.
From the Editor pulldown menu, select the Merge function. It will then prompt you; What feature do you want all selected features merged too?
This works in the exact same way that the dissolve tool works, except, it doesn't require matching records in a field to qualify for a dissolve. And the feature attributes are controlled by the user (by having control over which feature all other selected features are dissolved into).
That merge function operates in an entirely different way than the Merge Tool found in the toolbox.