The origin and history of "be full of oneself"

Its origin is unclear, but it has been in use since the mid-19th century. It is thought to have developed from the idea of being filled up with one's own self-importance, leading to an inflated sense of ego. Some believe the phrase may have originated from the image of someone literally being filled with themselves, such as an actor who has a high opinion of their own performance. Regardless of its origins, "be full of oneself" remains a common expression in modern English.