When Hela threw Loki out of the Bifrost, he landed on the planet Sakaar, eventually gaining the Grandmaster's favor over the course of a few weeks.
When Thor was imprisoned at the Grandmaster's palace, he and Loki quickly spoke to each other, and he was confused to learn that Loki had been on Sakaar for weeks. Grandmaster told Thor that time flowed oddly on Sakaar. He stated that anywhere else, he'd be millions of years old, then gave Loki an odd look. Loki is also seen in the spectator box with the Grandmaster during the fight between Thor and the Hulk, implying the high status he has earned.
Loki later informed Thor of his plans to eventually overthrow the Grandmaster. Having fallen out of favor with the Grandmaster after Thor and the Hulk's escape, Loki tried to capture them again for the reward money, but Thor thwarted his plan and left him behind while he, Bruce Banner, and Valkyrie set off for Asgard.
Fans generally believe that Loki hooked up with the Grandmaster in order to garner his favor. Although fics of the two can occasionally get rather dark. On AO3, Frostmaster is the most written ship for the Grandmaster.
|SHIPS||het||BobbiFitz • Brutasha • Clintasha • FitzSimmons • Fosterson • Huntingbird • Iron Widow • JessLuke • Kitscliffe • MayWard • NebulaRhodey • PeggySous • Philinda • Romanogers • Scarlet America • Spider Witch • Static Quake • Steggy • Winter Widow • Thunderwar • YoYoMack|
|slash||Capsicoul • FitzHunter • FitzMack • FitzWard • Hawksilver • Iron Husbands • IronStrange • Iron Winter • JackDaniels • Roquill • SamBucky • SamSteve • Science Boyfriends • Spiderlad • Stackie • Stony • Stucky • T'Chalcon • Thunder Science • ThunderShield|
|femslash||Cartinelli • Danbeau • Scarlet Widow • Simmorse • Valcarol|
|non-binary||FrostHawk • FrostIron • Frostmaster • Lokane • Scarlet Vision • Valki|
|family||Domestic Avengers • Iron Dad|
|CHARACTERS||m/f||Bucky Barnes • Natasha Romanoff • Steve Rogers • Tony Stark|