"Haggis is a dish containing sheep's 'pluck' (heart, liver and lungs), minced with onion, oatmeal, suet, spices, and salt, mixed with stock, and traditionally simmered in the animal's stomach for approximately three hours.
Haggis is a kind of sausage, or savoury pudding cooked in a casing of sheep's intestine, as sausages are. As the 2001 English edition of the Larousse Gastronomique puts it, "Although its description is not immediately appealing, haggis has an excellent nutty texture and delicious savoury flavour".[1]
Most modern commercial haggis is prepared in a casing rather than an actual stomach. There are also meat-free recipes for vegetarians.
The haggis is a traditional Scottish dish memorialised as the national dish of Scotland by Robert Burns' poem Address to a Haggis in 1787. Haggis is traditionally served with "neeps and tatties" (Scots: swede, yellow turnip or rutabaga and potatoes, boiled and mashed separately) and a "dram" (i.e. a glass of Scotch whisky), especially as the main course of a Burns supper. However it is also often eaten with other accompaniments, or served with a whisky-based sauce."
So, Sam, that answers your question, too. Neither one came first-they are served together.