This open-label, 2-part Phase I/ randomized Phase II multi-center study is conducted to evaluate the safety, tolerability, pharmacokinetics (PK), and clinical activity of afuresertib in combination with carfilzomib versus carfilzomib alone, in subjects with relapsed/refractory MM. Part 1 will evaluate 2 dose levels (125 milligrams [mg] and 150 mg of afuresertib) in 16 subjects (approximately 8 in each parallel arm) to determine an optimal dose of afuresertib for administration in combination with carfilzomib in Part 2. If neither of these dose levels are tolerated, an additional dose level of 100mg of afursertib in combination with carfilzomib may be explored in approximately 8 additional subjects. Part 2 was to investigate the safety, and clinical activity of the combination of afuresertib with carfilzomib (determined in Part 1) compared to carfilzomib alone, in approximately 100 subjects (50 in each parallel arm), however the study was terminated after the discontinuation of the single subject following the transition of the afuresertib development program from GSK to Novartis. The reason for the study termination is that the protocol defined study treatment was no longer aligned with the evolving standard of care.