How to create "masking effect" with which parts of object gradually show until it's fully visible?

In After Effects I can use an alpha matte to make the parts of an object appear gradually until it’s fully visible. How can I do that in Blender? Basically, I’d like to make some sort of intro like this.

Several ways. One is to make a material setup that mixes opaque shaders with a transparent one, and use a grayscale mask to mix them. Then animate the texture coordinates for the mask, or the mask itself.

The tricky part are texture coordinates so that it follows the curvature of a letter, which can be done by editing the UV layout, or by copying the UV’s from a helper object that is modeled for that purpose. The UV islands should be rectangular for all parts and align with the UV area, that way you can animate the mask by adding a value to either U or V coordinate.