Monarch started with former British Eagle directors who sensibly got out from that company a year before it went under. They began with Britannias from Luton, operating for main client Cosmos Holidays, also part of the same financial organisation, so giving them some vertical integration. In those days Cosmos were a decidedly bargain-basement tour operator, and Monarch shared that image, being the last major holiday airline to still be using prop aircraft to the Mediterranean after other had gone over to jets. They also, for several years, only operated out of Luton, Cosmos using other operators from elsewhere.
A notable feature of the whole operation is they are Swiss-owned, and follow a typical Swiss long-term careful business approach. Had they been British there would have been several leveraged buyouts of larger companies, huge spends on new fleets that would have benefitted a few along the way, and they would have been bankrupt. Probably two or three times.