When I was in high school, I have read in some magazine a variant of this "blood type personality theory".
To my amazement, that theory matched extremely well the personalities of all my colleagues from high school and of a few other friends and relatives, whose blood type I knew, unlike the predictions of personality based on astrology, which did not seem to match the known people more often than by random chance.
I have no idea which was the origin of that variant of the "blood type personality theory", but it was something very different from what is described in the Wikipedia article.
For instance people with type B blood were not classified as "spontaneous and creative" as in the Wikipedia page, but IIRC, as people who become mature in thinking at a lower age than the others, who are better at independent work, who may be stubborn and less influenceable by the opinions of others, who may be more trustworthy, but more introverted, and who may be inclined to careers in technical domains or in scientific research, or to military careers.
To my amazement, that theory matched extremely well the personalities of all my colleagues from high school and of a few other friends and relatives, whose blood type I knew, unlike the predictions of personality based on astrology, which did not seem to match the known people more often than by random chance.
I have no idea which was the origin of that variant of the "blood type personality theory", but it was something very different from what is described in the Wikipedia article.
For instance people with type B blood were not classified as "spontaneous and creative" as in the Wikipedia page, but IIRC, as people who become mature in thinking at a lower age than the others, who are better at independent work, who may be stubborn and less influenceable by the opinions of others, who may be more trustworthy, but more introverted, and who may be inclined to careers in technical domains or in scientific research, or to military careers.