Sir Iain Moncreiffe of That Ilk, 65, the chief of the Clan Moncreiffe and a lawyer, author, diplomat and genealogist who was once described as "one of those rare men who gives eccentricity a good name," died Feb. 27 at his home in London. The cause of death was not reported.

Lord Moncreiffe was the 11th baronet in a line created in 1685 and he had hereditary duties that dated back to 1248. Among the eccentricities for which this authority on Scottish lore and heraldry is remembered is his claim in 1970 to being the world's greatest snob.

He also asserted that even the way he held his whiskey glass dated back to 16th century ancestors. Occasions on which he perfected his form with whiskey glasses included nearly a year of sampling different blends of Scotch before he permitted a blend bearing the Moncreiffe name to go on the market. In dress he favored tartan trews, tartan ties and tartan jackets. His house bore a sign warning against a "giant wolfhound."

The style by which he was known is Saxon in origin. "Ilk" means "the same." Moncreiffe of That Ilk literally means "Moncreiffe of Moncreiffe."

Lord Moncreiffe was the head at various times of the two publications in which such information can be found. From 1977 to 1981, he was chairman of Debrett's Peerage and from 1983 until his death he was president of Burke's Peerage. He also served as Albany Herald of Arms and president of the Association of Genealogists and Record Agents. He was a captain in the Royal Company of Archers, which is also called the Queen's Body Guard for Scotland, and a member of the advisory committee of the Scottish National Portrait Gallery.

He took a master's degree at Christ Church College at Oxford University and a doctorate and a law degree at Edinburgh University.

During World War II, he was a captain in the Scots Guards and was wounded in action. After the war, he was a private secretary to Sir Maurice Peterson, the British ambassador to the Soviet Union. He later was a member of the Lloyd's of London insurance syndicate.

Lord Moncreiffe spent more than 40 years researching his own ancestry, tracing a family line back to 326 B.C. and King Pharnabazus, ruler of the Iberians. Among his ancestors, he found, was the Hungarian "Countess Dracula," Ersabet Bathory, who is listed in the Guinness Book of World Records as the woman who committed the most murders, 610 young virgins.

Among his books were "Blood Royal," "The Highland Clans" and "Royal Highness."

His marriage to the Countess of Erroll was dissolved in 1964.

He is survived by his wife, Hermione, and by two sons and a daughter by his first marriage. He is succeeded as baronet by his elder son, Merlin Sereld Victor Gilbert Moncreiff, a computer expert who lives in Hampshire. The younger son, Peregrine David Euan Malcolm Moncreiff, who lives in New York, becomes chief of the Clan Moncreiffe. His daughter is Alexandra Victoria Caroline Anne Hay.