The traditional chef's salad and Cobb salad share a few traits in common, but they are distinctly different salad dishes. Both are composed salads in which the ingredients are arranged before service and both contain lettuce and meats, but the similarities essentially stop there. There is also some dispute about the origins of each and several different people are credited with inventing or popularizing both salads. Whatever the origins, both are indisputably popular and they are a mainstay on the appetizer menus of restaurants all over the world.
According to food historians, the origins of the chef's salad may lie as early as the 17th century, when people prepared a dish with lettuce and meat known as salmagundi. This sounds a great deal like modern chef's salad, which is usually served with sliced hard boiled eggs as well. Chef Louis Diat who worked at the Ritz in the 1940s is often given the credit for popularizing the chef's salad, but this dish was on many menus prior to the 1940s in a frame which would be recognizable to today's diners.
The Cobb salad, by contrast, was developed in the 1930s. The Brown Derby Restaurant claims the fame for the invention of the Cobb salad; according to the restaurant's history, the salad was invented by Bob Cobb in 1937 when hungry diners came in late and only a hodgepodge of ingredients was available. The salad became popular and was added to a menu. It's also highly likely that the development of this salad was inspired by the chef's salad, which would have been known in some form to Bob Cobb.
Like a chef's salad, a Cobb salad contains lettuce, meats such as bacon, chicken breast, and ham, and hard boiled eggs. However, it can contain a mixture of lettuces, and it also usually contains bitter greens, which makes it different from a chef's salad. In addition, the Cobb salad has avocado, tomato, and roquefort cheese.
Both salads tend to be filling because of the meats, and the flavor and precise ingredients can vary depending on the tastes of the cook. The Cobb salad tends to have a more complex flavor thanks to the cheese, bitter greens, and avocado, and it may have a creamier taste because of the fats in the avocado. Some restaurants have both on the menu and may provide specific information about the ingredients they use upon request, while others may prepare one or the other.