Hendrickson was the German (later Dutch) member of the Blackhawk Squadron. He first appeared in Military Comics (Quality Comics, 1941 Series) #2 (September 1941). He was called Hendrick in his first appearance only, was unnamed in issues #3-4, and was finally called Hendrickson in issue #5 (December 1941). Hendrickson may also have been one of the unidentified members of the Blackhawks that appeared in issue #1.
Hendrickson was originally depicted as German, and consistently used German words and phrases from 1941 through 1968. According to Blackhawk (Quality Comics, 1944 series) #71 (December 1953) Hendrickson was from "Democratic Germany", and according to issue #85 (February 1955) from "Free Germany". He was first identified as Dutch in a text story in issue #21 (Oct 1948). In issue #50 (March 1952), he was said to have escaped from a Nazi concentration camp just prior to joining the Blackhawks, however his nationality was not given. He was again referred to as being Dutch in Blackhawk (DC, 1957 series) #198 (July 1964). The inconsistency was finally addressed in the letters page of issue #244 (January-February 1976), which stated that he was "Of Dutch descent, it is believed that Hendrickson spent much of his childhood in Germany". When Mark Evanier rebooted the feature in issue #251 (October 1982), Hendrickson was established as being from Holland, and issue #253 (December 1982) made it clear that he no longer had any connection to Germany.
Hendrickson's first name, Hans, was revealed in Blackhawk (Quality Comics, 1944 series) #75 (April 1954).
Hendrickson's daughter, Elsa, was introduced in Blackhawk (DC, 1957 series) #245 (March-April 1976). Issue #253 (December 1982) introduced his wife, Violet, who died in 1939 in a Nazi attack on Rotterdam.