Whether it's a reverential nod to a respected peer or a crafty swipe at a rival developer, there are countless examples of games being referenced in other games. Sometimes they're hidden away as Easter eggs, whereas at other times they're much more obvious and form part of the main story itself. Here are ten of our favourites - let us know yours in the comments.
1. DRIVER... IN GRAND THEFT AUTO
The GTA series has always had its finger on the pulse of popular culture, with Rockstar taking subtle (and not-so-subtle) pot shots at everything from fast food restaurants to the internet. However, the Driver games, and main character John Tanner, were given special attention.
The ribbing started in Grand Theft Auto III when you were ordered to kill a target named Tanner, described as a "strangely animated undercover cop" who is "more or less useless out of his car". This was a direct reference to Driver 2, as - in that game - Tanner could leave his car for the first time, but the way he moved was... odd. Never one to let an opportunity slip, Rockstar emphasised Tanner's unconvincing gait by giving him the animation set of a female pedestrian.
During the "Autocide" mission in Grand Theft Auto: Vice City, you had to eliminate members of a European gang planning a bank robbery. Each of the targets is named after a character in another sandbox game, including DBP Security worker Dick Tanner. But this time Rockstar didn't just stop with Reflections. The other gangsters are Mike Griffin (Mace Griffin, Mace Griffin: Bounty Hunter), Nick Kong (Nick Kang, True Crime: Streets of LA), Marcus Hammond, Franco Carter and Charlie Dilson (Mark Hammond, Frank Carter and Charlie Jolson, The Getaway.)
Finally, as part of the Grand Theft Auto: San Andreas mission "Madd Dogg's Rhymes" you have to sneak through Madd Dogg's mansion while avoiding his personal security. When you reach a bar area, the camera cuts to a guard playing an unseen videogame and shouting "This sucks! I mean how could Refractions mess up so bad? Tanner, you suck ass!" Clearly, the target was Reflections, who'd released Driv3r to generally poor reviews earlier in the year.
2. GRAND THEFT AUTO: VICE CITY... IN DRIV3R
Grand Theft Auto's repeated mocking of the Driver franchise certainly hadn't gone unnoticed by Reflections, and by the time it developed the third instalment in the series the studio decided to get its own back. To that end, collectibles were added in the form of hidden characters called Timmy Vermicelli, spoofing Vice City's main protagonist Tommy Vercetti.
With nuclear-orange fake tan and garish pink Hawaiian shirts, they traded off Vice City's Miami setting, but the Timmies also sported inflatable water-wings on their arms, referencing the fact that GTA players weren't able to swim at that point - whereas, in Driv3r, Tanner could.
There were 30 Timmies to hunt down and eliminate to unlock various bonuses, but they proved to be formidable foes. They would aggressively shoot on sight and were armed with powerful rifles, playing up to GTA's violent reputation, meaning a sneaky approach was required to get in close and take them out.
3. METAL GEAR SOLID... IN HITMAN: ABSOLUTION
A number of games are referenced in Hitman Absolution's copious Easter eggs, including multiple appearances by IO's own gruesome twosome, Kane and Lynch. However, a much less obvious gaming nod can be found in the Test Facility section of the Death Factory mission.
In the land mine testing area head through the garage door opening in the building fašade, then turn left and follow the corridor to the end. Here you'll find one of the test pigs in a crate happily chomping away on a bowl of food, but if you shoot it something quite neat happens.
Pull the trigger and a large exclamation mark appears above the pig's head - the iconic symbol, of course, from the Metal Gear Solid series. After that, it then bounces across the screen to the sound of laughter before being shot. A comment on a YouTube video from Hitman: Absolution UI Designer Mehrzad "Baconshot" Beiknejad confirmed he instigated this Easter egg to represent his nickname - and as a reference to Metal Gear as he loves the games.