The company said Bulat had left for "personal reasons".
Bulat joined from Unilever as marketing director in November last year and reported to Samsung Mobile’s UK managing director, Simon Stanford.
He had previously worked at Johnson & Johnson and Reckitt Benckiser.
Bulat joined Samsung as it rolled out its "smartphone for everyone" strategy.
He had responsibility for mobile and tablet devices, including the Galaxy Tab, which was supplemented with £200 of free media in January.
Samsung and rival HTC are known to be moving heavily into social media as part of their marketing push.
Samsung also produced Google's Nexus S phone, the first to feature the Android 2.3 operating system.