Reuben Mattus, the Polish immigrant who stuck an umlaut on a nonsensical name and parlayed the exotic result into the multimillion-dollar company that sold Haagen-Dazs ice cream, died on Thursday in the North Broward Medical Center in Deerfield Beach, Fla. Mr. Mattus, who lived in Cresskill, N.J., was 81.

Mr. Mattus suffered a heart attack while on vacation, said a daughter, Doris Hurley.

Starting as a teen-ager and working first out of a horse and wagon, Mr. Mattus peddled the Mattus family's homemade ice cream for more than 30 years to small candy stores and neighborhood restaurants in the Bronx, expanding his business gradually. The financial rewards were modest until 1959, when he hit on the idea that would make his fortune.

Correctly deducing that a large share of ice cream lovers in New York would be willing to pay for something they perceived as different, even evocative, and maybe better, Mr. Mattus came up with the name Haagen-Dazs, wanting it to sound cold, clear, luxurious and Danish. A map of Scandinavia was printed on its carton.

But the name is not Danish, indeed the umlaut does not exist in Danish, and the name means as little in that language as it does in English. More Butterfat, Less Air