More like Dear Sir

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The Stainless Steel RatSeries
series21 books1957
completed
Space opera, adventurous in tone, set in far future and space.
“An adolescent boy on a dull planet resolves to live by his wits outside the law, and enacts a plan which leads to risk and reward.”
from the catalogue
Start with A Stainless Steel Rat Is Born →
Leland HaleSeries
series4 books1957
completed
Humor, set in far future and other star systems.
Start with To Make a Hero →
The Pirates of ZanNovel
Murray Leinsterstandalone novel1959
Space opera, about pirates, set in other star systems and far future.
FoolSeries
series4 books2009
Humor.
Start with Fool →
The MacNair of MacNairSeries
series3 books1987
completed
Time travel.
“The protagonist is a dapper, clever con man who, although born to humble origins in Bangor, Maine, United States, calls himself Sir Kevin Dean de Courtney MacNair of MacNair.”
from the catalogue
Start with Napoleon Disentimed →
The High CrusadeNovel
Poul Andersonstandalone novel1960
About aliens and war, set in british isles and medieval.