Someone or something that causes or produces an effect.(noun)
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Use "causer" in a sentence
"Through our brief examination of nature, we have seen that the causer is a superior intellectual being who incorporated intelligence, reasoning, planning, design, and order into all that he created."
"(the boulder "doesn't want to" -- thinking of the cave person as a "causer" is a very naive view)."
"Actually, yours are even more illogical since "because" implies a cause implies a causer which you claim does not exist."