Guinan

Guinan was a mysterious 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 (so named because on a Galaxy-class Federation ship like the Enterprise, it is located on Deck 10, Section 1.)

Biography
There was a reason why Picard brought the Eleventh Doctor to Ten Forward. As an El-Aurian - a race of "listeners" scattered by the Borg that Data had suspected were time sensitive - Guinan was no stranger to sensing disturbances in time. For example, she correctly sensed an alternate timeline featuring a war with the Klingons that emerged when a temporal rift opened to reveal the ship's immediate predecessor, the Enterprise-C (shown in the Next Generation episode "Yesterday's Enterprise".)

In 2366, she 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, and they found that they had a familiarity with each other that both knew they shouldn't otherwise have, which they recognize as due to their shared ability to sense disturbances in time (the Doctor due to being a Time Lord and Guinan due to being El-Aurian.) They also realised that the Cybermen had somehow altered history in order to bring their respective universes together and forge an alliance with the the Borg. (COMIC: Assimilation²)