Chances are that you have heard about Lycamobile, either for their cheap local and international call rates or because of some wrong reasons for which they have been in the news recently. They claim to be world's largest International MVNO, which is most likely true as I can't think of any other competitor this big.
There are quite a few different companies in Lycamobile group as can be seen above. More details are on the group website here.
In addition, Lyca group has a whole range of other companies, including Lyca production which is involved in producing movies. More info on Wikipedia here.
Finally, the picture below is a slide from Mobile World Congress 2018, showing the reach of Lycamobile.