|Wendayne and Forrest J. Ackerman (sitting,|
with Ray Bradbury at the podium), 1967 [source]
In the meantime, however, this article, "Peacelord of the Universe: Perry Rhodan in English" [link], being as far as I can tell via an Internet search originally from ca. 2011, gives a very thorough overview of the history of the German-born Perry Rhodan pulp science-fiction series in English.
"That Rhodan came to be published in English at all is due to [German co-creator Walter] Ernsting’s recognition of its potential in that market and his friendship with the man who was to become the series’ ‘English language representative’ and managing editor during its 1969-1978 English run. Forrest J Ackerman was still an active contributor to SF fandom rather than prodom back in the 1950s when he helped found the Science Fiction Club Deutschland alongside Ernsting, then still trying to break into the German market as an author. Because the only SF being published in Germany in the fifties came from American and British writers, Ernsting wrote his first novel under the American-sounding pseudonym ‘Clark Darlton’ and pretended he had merely translated it from English; consequently he was saddled with the pen name throughout the rest of his career.
"In 1965 Ackerman and his German-born wife Wendayne met Ernsting in person for the first time at a book fair in Europe and spent a few days as his houseguests. During their visit Ernsting made Forry a present of a complete set of the Perry Rhodan series he had created in 1961 with noted German author KH Scheer (Ernsting was responsible for the name, supposedly from a combination of Perry Mason and Japanese movie monster Rodan, ‘Americanized’ with the addition of the H). He also suggested that Ackerman could introduce Rhodan to the US market and, in a famously oft-to-be-repeated quote, that 'Wendy could translate it in her spare time'. By 1975, when the series was appearing in English three times a month, Wendy was perhaps wondering what she had let herself in for...."
Read more here [link].
Cheers!, and Ad Astra!