James John Howard Gregory lived from 7 November 1827 to 20 February 1910. He ran an important seed catalogue business  which helped introduce vegetables now considered heirloom stock such as the Hubbard Squash and the Burbank potato.
Brillat-Savarin, while not a chef, has been one of the most influential food writers of all time. He is known for his book Physiologie du Goût (translated variously into English as The Physiology of Taste, The Philosopher in the Kitchen, etc.) Brillat-Savarin's goal was to raise cooking to a level of true science.
Jean-Pierre Clause is known now as the creator of Pâté de Contades. Cynics point out that really what Clause really achieved was to take a peasant dish, dress it up, and make all the rich people swoon over it.
Jean Paré (pronounced Gene Perry) is the world's top selling cookbook author, with 23 million copies of her books sold as of 2006, though Britain's Delia Smith comes a close second. And Jean got a late start -- her writing career didn't begin until she was 54.
Jennifer Paterson gained overnight fame as one of the two principals on the TV series called Two Fat Ladies, and as co-author of the accompanying cookbooks. She also wrote columns for The Spectator and The Oldie, did TV appearances on Food and Drink on BBC 2, and was often on the BBC Radio 4 programme called Questions of Taste.
Julia Child was the person who more than anyone else brought French cooking to North American middle-class households as a TV personality and author. She is only familiar to North Americans, though; she remains mostly unknown in Britain and in Europe.