Aston Villa in 1886 were the first team to have worn those colours.

Unfortunately there are no definite records recording the thinking behind the original choice, there are suggestions that as their sponsor William McGregor was a draper he had too much fabric of those colours, or that as he was a Scot the choice was a nod to the maroon of Hearts and the blue of Rangers.

Aston Villa were one of the best side in the country for a while winning the league 5 out of 7 years around the end of the 19th Century, start of the 20th.

There are stories to justify why other clubs copied their strip, Burnley admit it was a tribute/inspiration thing, West Ham claim it was because an Aston Villa player lost a bet and they took the kit (probably apocryphal), but many clubs just starting out didn't keep full records of why they did things, so it's mostly folk lore.

(mods: I'm aware this is solid reference light, so if it has to go, no hard feelings)