The earliest case I'm aware of dealing with "corporate personhood" is The Rev John Bracken v. The Visitors of Wm & Mary College, from 1790, which is discussed in the linked article  (page 434 discusses the founder's wishes, treating the corporation as an extension of the will of its founder, through its charter.) The rest of US case law, long before Citizens United, follows this same pattern -- corporations, being "merely associations of individuals united for a special purpose" , function legally as individuals in many ways, with the right to speak and own property and other such things that fit with the purpose for which they are founded.
A relevant quote from US case law: "The principle at stake is not peculiar to unions. It is applicable as well to associations of manufacturers, retail and wholesale trade groups, consumers' leagues, farmers' unions, religious groups, and every other association representing a segment of American life and taking an active part in our political campaigns and discussions .... It is therefore important -- vitally important -- that all channels of communication be open to [all of the above types of associations] during every election, that no point of view be restrained or barred, and that the people have access to the views of every group in the community." 
 Pembina Consolidated Silver Mining Co. v. Pennsylvania, 1888 https://supreme.justia.com/cases/federal/us/125/181/
 United States v. Auto Workers, 1957 https://supreme.justia.com/cases/federal/us/352/567/