You’re an expert on Aliens and their cultures. At least the ones humanity have contacted. For first contact situations, your extensive experience will give you the edge in (hopefully) making peaceful contact.
Possible backgrounds could be:
- A stint in the diplomatic corps
- Having toured on a tramp frieghter
- Galactic Hitchhiker, trying to see the Marvels universe for less than 30 Altairan Dollars a day