Worf was another surprise that TNG gave us, we hadnt expected that!  Orphaned as a young child Worf was raised by human foster parents to eventually join Starfleet and the Enterprise as a Bridge Officer.  As an adult, his mannerisms and personality, as well as his innate sense of honour, became more Klingon than human.  His was a complex personality but his courage and loyalty made his an easy character to like.