Olivier salad is a Russian salad with variable ingredients, but it is typically made with chopped vegetables, meat, and mayonnaise. The key ingredients include diced potatoes, vegetables, eggs, chicken, or ham. This salad is one of the most important appetizers at the New Year's salad buffets in Russia, as well as in some of the other countries of the former USSR.
The original was invented in the 1860s by Lucien Olivier, a chef in the popular Moscow restaurant called L'Hermitage. Olivier guarded the recipe until he died, but it is believed that the recipe was stolen by an employee who watched the chef at work, so the salad is still made today.
Another theory says that the recipe for the new Olivier salad was developed by one of the restaurant's customers who wanted to keep the salad alive after the chef passed away. Olivier salad as we know it today is nothing like the original version, because it was called game bird mayonnaise, made with gourmet ingredients such as black caviar, capers, hen, and crayfish tails.
Over time, the salad evolved and most of the gourmet ingredients have been replaced with more common ones such as peas, chicken, ham, and pickles. Today, the variations are endless, but most Russian chefs agree on one thing: adding carrots to the Olivier is a heresy.
Interestingly, Olivier salad is also sometimes called Russian salad, while the meatless version is called French salad or francuska salata, probably due to the French name of its creator. The Spanish version is known as ensaladilla rusa.
It is so popular in Spain that it's an important part of the Spanish gastronomy as well as being a staple in schools and summer camps all over the country. Ensaladilla rusa is also one of Spain's most popular tapas – in some cases, it's even served free of charge if you order a beer.
There's also the Piedmontese insalata russa, typically consumed as an appetizer, and with many variations, so the salad might also include ingredients such as pickled cauliflower, anchovies, and tuna. Interestingly, in the Italian municipality of Carrù, tuna is an obligatory element of the salad.
https://www.tasteatlas.com/olivier-salad