Trillian

Trillian is humanoid, slim, darkish, with long waves of dark hair, a full mouth, an odd little knob of a nose, ridiculously brown eyes (p.37). Her real name is Tricia McMillan.
She is Zaphod's girlfriend. Zaphod takes Trillian with him after he has met her on a party on earth.  She steals the "Heart of gold" with Zaphod and travels through the galaxy. Her only reminder of the earth are two white mice.
She is very intelligent. On earth she studied maths and astrophysics, so it's no problem for her to understand the "Heart of Gold" and the other things in the galaxy.

(!!!In the TV-series Trillian doesn't look like she is described in the book!!!) 

by Pia