Refers to the event in 'Age of Empires 2' during the last scenario of the Celtic campaign when William Wallace comes to shore to aid you in fighting the English.

Alternative meanings:

To express feeling that victory is at hand.

(also) When someone important arrives,
or comment to express excitement of help coming one's way.
Dude 1: This blows, we're stuck in the parking lot and your car is busted.

Dude 2: *Calls his friend*

*Friend arrives*

Dude 1:"Wallace has come"
by anti_muppet_crusader October 13, 2011
Get the Wallace has come mug.