Kuwait’s sovereign wealth fund, the world’s oldest and one of the largest, has played a key role in preparing OPEC’s fourth-largest producer for a post-oil future and helping prop up the economy as it was battered by the pandemic. The $769 billion Kuwait Investment Authority is also a leading global investor, with holdings in BlackRock Inc. and Mercedes-Benz Group AG. In a rare move, it ousted the head of its London arm in July, sending shock waves through the normally sedate and secretive world