A Meta Establisher is someone who plays a champion and other people for whatever reason, follow the lead of the Meta Establisher and play the champions that the meta Establisher is playing. Below are a few reasons why Faker has been an incredible Meta Establisher in the midlane throughout his career.
Faker has long been considered one the the best League of Legends player of all time. Although his statistics on every category are beyond impressive, one aspect of his game that should not be overlooked is the respect other players have for him. Faker has established the meta in the mid lane almost since he came into the scene, some of it has to do with his ability to quickly figure out what champions are overpowered after a patch is introduced, but the respect other players have for him, also contributes to his Meta Establisher history.

Xerath:

Faker introduced Xerath into the scene worsening the wave-clear meta where Xerath and Ziggs were prioritized. Throughout the next few months Xerath was the top pick/banned champion across all regions and was introduced by Faker.

Ryze:

Faker introduced Ryze into season 5 Worlds. It was not until the tournament was over that other teams realized that the champion was overpowered, yet Faker figured it out before the tournament started and continued to use it even in the finals against Koo Tigers.

Karma: 

Faker introduced Karma into the scene. The champion was used in the midland for a short time, yet other regions(notably NA) picked it up. Faker only played Karma once, funnily enough lost that game. However, Karma was a contested pick in NA, exacerbating the situation due to the fact that Bjergsen got a pentakill on her.
Faker played his first competitive game of season 6 with Corki. Although he has not played any other games with the champion, Corki has become a priority pick in NA, and has seen some play in other regions.

Viktor:

The champion that was more established by one player in my opinion was Viktor in season 5. Faker prioritized this champion picking it into anything last season. This is something very uncharacteristic of Faker since his incredibly big champion pool, means that he typically does not highly prioritize a single champion. However, his undefeated record on the champion, making it one of the champions that he is undefeated on having played the most games on(used to be LeBlanc, but he lost with her at MSI). The interesting part is that every region prioritized Viktor as well last season when the midlane meta was composed of :Cassiopia, Azir and Viktor. Yet, LMS region and NA had negative win rates on the champion despite prioritizing it. NA had more than ten games played on Viktor and continued to first pick/ban just because Faker had tremendous success on the champion.

LeBlanc:

Arguably Faker’s most successful champion is LeBlanc, one of the champions that requires mastery in order to play at the competitive level. Last season before MSI, around spring time, every team banned LeBlanc against SKT. Yet, anyone else who attempted to play the champion, was not nearly as impressive as Faker was. No other player was feared for his LeBlanc, yet teams had to ban it against SKT and it took the most anti-LeBlanc team composition to finally defeat Faker on that champion. Although very few players followed Faker’s lead around this time, and even fewer had success on her, LeBlanc deserves an honorable mention because Faker was the only one that figured out how to effectively use her. The champion was later nerfed and it can be said it was a target nerf towards Faker as he alone made the champion look overpowered.

Honorable mentions:

There are many more examples like mid Riven, Zed, Ahri and Ezreal that Faker has in some way or another influenced the meta with. They deserve an honorable mention, but they were either not introduced by Faker, or other players did not follow Faker and played the champion enough.