The one who's being celebrated (e.g., @ a BD party) (sometimes referred to as the birthday boy/girl) [duplicate]
Guest of Honor would work for either gender at any big party in their honor.
If you are looking for a single word it is honoree
hon•or•ee (ˌɒn əˈri)
n. a person who receives an honor, award, or special recognition.
Specifically in the case of a distinction or achievement, it is laureate.
n. 1. One honored or awarded a prize for great achievements especially in the arts or sciences: a Nobel laureate. A poet laureate.