La Forge is attacked by an alien
Quantum singularity lifeforms were an alien species.
In 2369, these lifeforms inadvertently caused a rupture in time when they damaged a Romulan warbird. The USS Enterprise-D responded to a distress call by the Romulans. When the Enterprise-D attempted an energy transfer to assist the Romulans, it caused a disruption, freezing both vessels in time. Captain Picard along with Deanna Troi, Data, and Geordi La Forge, who were not on the ship during the disruption, were able to reverse the effects of the disruption and restore the proper time.
The male alien told the crew that they were protecting their infant which was trapped in the warp core of the Romulan warbird which used a black hole as energy source. (TNG: "Timescape")