Guinan

Guinan is a character on Star Trek: The Next Generation portrayed by Whoopi Goldberg.

She is a member of a species of "listeners" that was scattered throughout the galaxy when the Borg destroyed their homeworld. She is known to have visited San Francisco on Earth in the late 19th century, where she assisted the crew of the Enterprise-D (who had traveled back in time from the 24th century), meeting Jean-Luc Picard for the first time.

Guinan was aboard an El-Aurian transport vessel trapped in an energy ribbon known as the Nexus for some time. In 2293 she was "rescued" from it by the Enterprise-B. Roughly seventy years later, she ended up on the Enterprise-D, serving up drinks and advice in the Ten-Forward lounge.

Besides the Borg, Guinan has some other enemies, such as Q, who has some history with Guinan and was responsible for introducing the Borg to humanity (prompting the tragedy at Wolf 359 and the events in Star Trek First Contact).

The Star Trek Project

Guinan is an El-Aurian "Listener" who is over 600 years old and works aboard the U.S.S. Enterprise in Ten-Forward as the hostess. Although she is an amazing listener and dispenses advice to anyone in need, she rarely speaks of her past and little is known about her. Captain Picard asked her aboard the Enterprise in early 2365 and ever since she has been an informal counselor to the ship's staff and even provides real alcoholic beverages on special occasions despite Starfleet's regulations.

In 1893, Guinan came to Earth to hide from her father. Not long after, she visited San Francisco and assisted the crew of the Enterprise during a mission of theirs which had them transported into the past. It was during this meeting that she first met Jean-Luc Picard and they became friends. She first encountered Q in the 2160s, although she was known by a different name at the time, and they both loathe the other. Her people were attacked by the Borg a century later while she was away, but somehow she ended up on the refugee-filled S.S. Lakul about 27 years later near Earth in 2293. She was partly trapped in the Nexus ribbon that caused the apparent death of Captain James T. Kirk and after the incident she developed a "sixth sense".

As for her personal life, she had an imaginary Tarcassian razor beast as a childhood pet whom she still talks to when she has the time. Guinan has been married twice and has "a lot" of children, even one who had trouble listening for several hundred years. Her family also incudes a 700+ year old father and a family "black sheep", Uncle Terkim. Guinan's main personal enemies are Q and the Borg, although she lightened up after meeting Hugh after he was cut off from the collective. Picard is one of her closest friends and their relationship goes "beyond friendship and beyond family."

Sources:
http://www.startrek.com/library/individ.asp?ID=112466