Final answer:
Alfred Adler was the psychologist who suggested that birth order influences personality, with older, middle, and youngest siblings potentially developing different traits based on their family position, although this theory hasn't been conclusively proven by research.
Step-by-step explanation:
The psychologist who suggested that birth order shaped personality was Alfred Adler. Adler was one of the neo-Freudians who agreed with Freud on the importance of childhood experiences in personality development but placed less emphasis on sexuality, focusing more on social influences and cultural effects on personality. Adler's birth order theory proposed that an individual's position in the family, such as being the oldest, middle, or youngest child, can impact their personality traits. Older siblings might become overachievers to compensate for the loss of undivided parental attention, while the youngest could be more spoiled, and the middle child might navigate between minimizing the extremes of the oldest and youngest. However, it is important to note that research has not conclusively confirmed the specifics of Adler's hypotheses about birth order effects on personality.