William C. Patrick III made enough germs to kill everyone on earth many times over. Then, after putting aside those living weapons, he worked for nearly four decades to build defenses against them, to better protect the United States from biological attack.

A scientist, Mr. Patrick made germ weapons for the American military from 1951 to 1969. He produced tons of deadly agents, like the microbe anthrax, which, when inhaled, causes fever, cough, vomiting, chills, shock and coma, usually ending in death. He received five patents, all of them granted secretly.

His production of these microscopic killers ended in 1969 when the Nixon administration decided that the nation could survive the cold war without the benefit of Mr. Patrick’s black art. He then devoted himself to germ defenses, working for the government and as a private consultant.

Mr. Patrick, 84, died of bladder cancer on Oct. 1 at a nursing home in Frederick, Md., said his wife, Virginia.