Guinan

Guinan was a time sensitive native to a parallel universe. She worked as a bartender in the 24th century in the USS Enterprise-D's lounge and recreation facility known as Ten Forward.

When the Cybermen of the cyber-web invaded the Federation's universe, it began merging the reality with N-Space who, in 2366, began receiving memories of things that she felt she should not actually remember. When the Eleventh Doctor arrived on the Enterprise and experienced the same problem in 2368, Captain Jean-Luc Picard brought him to Ten Forward to meet Guinan. Speaking, the two time sensitives found each other familiar yet both knew that they should not. Recognising this as a disturbance in time, they deduced that the Cybermen's alteration of history in their forging an alliance with the Borg.

When the Cybermen reneged on the alliance, the Borg offered to ally with the Enterprise to defeat their common foe. When Picard refused, Guinan visited his ready room informing him of the Cybermen threat and explaining Picard's time as Locutus of Borg to the Doctor. Despite this, Picard refused to ally with the Borg, justifying his decision on the basis that the Enterprise could not catch up to the Cyber-Fleet and even if it could, it didn't have the firepower to destroy a fleet. (COMIC: Assimilation²)

Behind the scenes

 * Assimilation² depicts Guinan with the likeness of actor, who originally portrayed her in Star Trek: The Next Generation.