Seagram's 7 Crown Whiskey is a blended American whiskey that's most famous for its signature cocktail, the Seven and Seven. It's not a particularly complex whiskey, but it's affordable and designed for mixing. Seagram's 7 is a mainstay in bars around the world, and does well in all kinds of highball cocktails.
Seagram's Seven was most popular in the latter half of the 20th century, particularly the 1970s, but has steadily declined ever since as other spirits have flourished. But it's cheap, decent, and known by every bartender you'll come across, so it has remained a staple of drinking culture regardless.