Tom Collins is a classic cocktail hailing from London. It's made with a combination of gin, lemon juice, sugar syrup, and soda water poured into an ice-filled glass. It is believed that this refreshing drink was created by the head waiter at a London restaurant, and the drink was named after him.
Although it was originally made with jenever, these days the cocktail should ideally be made with Old Tom Gin, which is a bit sweeter than London Dry Gin used for John Collins. The first recipe for Tom Collins was printed in Jerry Thomas' book The Bartender's Guide in 1876.