Yazdegerd III
One strategic success was his sundering of the Byzantine-Sassanid alliance in 636, when Emperor Heraclius and Emperor Yazdegerd III allied against their common enemy. He was lucky in that the Persian Emperor Yazdegerd III couldn't synchronize with Heraclius as planned. Omar fully availed himself of the opportunity by inducing the Byzantines to act prematurely. This was contrary to the orders of Emperor Heraclius, who presumably wanted a coordinated attack along with the Persians. Omar did this by sending reinforcements to the Roman front in the Battle of Yarmouk, with instructions that they should appear in the form of small bands, one after the other, giving the impression of a continuous stream of reinforcements that finally lured the Byzantines to an untimely battle. On the other hand, Yazdegerd III was engaged in negotiations that further gave Omar time to transfer his troops from Syria to Iraq. These troops proved decisive in the Battle of Qadisiyyah.