Question: What phone series serves as the successor to phones officially unveiled at the "Samsung Unpacked 2015" event?

Passages:
The Samsung Behold SGH-T919 is a touch-screen, 3G candybar-style mobile phone introduced by Samsung late in 2008.  The Behold is one of the first Samsung mobile phones released to have a touch-screen along with the Samsung Omnia, the Samsung Instinct, the Samsung Eternity, and the Samsung Tocco.  The Behold is the "American" release of Samsung Tocco, which is only sold in Europe, Asia and Australia so the features and design of both of these phones are similar.  Some of the Behold's biggest competitors were Apple's iPhone, T-Mobile G1 (HTC Dream), LG Dare, Samsung Instinct, and Samsung Eternity.  It was only available only to customers of T-Mobile. Samsung Galaxy S Duos 2 is a version of Samsung Galaxy Trend Plus with dual SIM Android smartphone, produced and marketed by Samsung Electronics, which serves as an immediate successor to the original Galaxy S Duos, which is made in second quarter of 2012.  Unveiled on 30 November 2013 at some Asian markets, it was initially released on December 5, 2013 in several countries.  In contrast with other dual sim Samsung models, this phone is a part of the high-end "S" series, this is why it is marketed as a part of the "Galaxy S" family.  Despite being called as a direct successor to the original S Duos phone, external and physical design of the model is identical to the original model, placing emphasis on internal upgrades such as upgraded processor and updated Operating System software. The Samsung E900, introduced in 2006, is a high-end mobile phone and is derived from Samsung's D500-D600-D800 series of slide phones.  It is of a slide-up design and has touch-sensitive keys, similar to the LG Chocolate (KG800).  It was one of the most popular phones at the time but was discontinued late 2007 when buyers then turned their attention to the Samsung D900i, followed by the Samsung U600, which was the slimmest phone by Samsung with a thickness of 1.09 cm until the E840 was released. Samsung Galaxy S6, Samsung Galaxy S6 Edge, and Samsung Galaxy S6 Edge+ are Android smartphones manufactured and marketed by Samsung Electronics.  The S6 line serves as a successor to the Galaxy S5.  The S6 and S6 Edge smartphones were officially unveiled in the first "Samsung Unpacked 2015" event at Mobile World Congress on 1 March 2015, while the bigger S6 Edge+ was officially unveiled together with the Samsung Galaxy Note 5 in the second "Samsung Unpacked 2015" event at New York on 13 August 2015.  Alongside the S6, Samsung also unveiled the S6 Edge (and later on the bigger S6 Edge+), a variant whose screen is wrapped along the sides of the device; the curvature is usable for several additional features.  The Galaxy S6 and S6 Edge were released on 10 April 2015 in 20 countries while the S6 Edge+ was released on 21 August 2015 in 20 countries. The Samsung REX series is a range of Samsung smartphones and feature phones, ranging from low to mid-end phones, running a Java-based operating system with Samsung's TouchWiz user interface.  It is currently one of the Samsung line of devices that are aimed at the budget phone market alongside lower end Samsung Galaxy devices.  Its main competition includes the Nokia Asha range and Firefox OS. Samsung Galaxy S7 and Samsung Galaxy S7 Edge are Android smartphones manufactured and marketed by Samsung Electronics.  The S7 series serves as the successor to the Galaxy S6, S6 Edge and S6 Edge+ released in 2015.  The phones were officially unveiled on 21 February 2016, during a Samsung press conference at Mobile World Congress, with a European and North American release on 11 March 2016. The Samsung SGH-D500 is a slider-style mobile phone created by Samsung.  It was announced in Q4 2004 as a replacement to the popular Samsung E800.  It has a 1.3 megapixel digital camera with an integrated LED flash.  The phone can be purchased in various colors such as black, grey/silver, silver/white, silver/blue, black/blue, and black/silver.  The D500 won the prestigious award "the worlds best cellphone" at the 3GSM world congress in Cannes, 2005.  The SGH-D500 was popular with consumers because of the large screen-size to front-surface ratio, the smooth button and sliding action, powerful flash, and good video/photograph/sound quality.  The D500 was regarded as compact and as having a good feature set for its time.  Samsung experienced remarkable success with the introduction of the D500 and has therefore introduced several other slider-style mobile phones in recent years, some fairly successful, others not so much.  This phone helped to popularise the 'active' sliding phone concept across all brands.  The SGH-D500 has been succeeded by the Samsung SGH-D600.  There is a very similar variant handset, the SGH-D500E. The Samsung Galaxy Tab 8.9 is an Android-based tablet computer designed and manufactured by Samsung, introduced on 22 March 2011 at CTIA wireless convention in its Samsung Unpacked event in Orlando.  It is part of the Samsung Galaxy Tab series, and features an 8.9-inch display and a 1 GHz dual-core Nvidia Tegra 2 processor. The Samsung Galaxy Gear is a smartwatch produced by Samsung Electronics in the Samsung Gear family of devices.  Unveiled during a "Samsung Unpacked" event in Berlin, Germany on September 4, 2013, the device serves as a companion for all Samsung Galaxy smartphones and tablets which run Android 4.3 or newer; it was released on September 25, 2013.  Originally released as an Android-based device, Samsung replaced the operating system with Tizen through the May 2014 software update. The Samsung ATIV S is a touchscreen, slate smartphone manufactured by Samsung Electronics running the Windows Phone 8 operating system, upgradeable to Windows Phone 8.1.  The ATIV S is Samsung's first Windows Phone 8 device, and one of the first devices under its ATIV series of Microsoft Windows-based products.  It was shown at the IFA 2012 in Berlin and was the first Windows Phone 8 device to be officially unveiled, ahead of the Nokia Lumia 920.

Supporting sentences:
 The S7 series serves as the successor to the Galaxy S6, S6 Edge and S6 Edge+ released in 2015. Samsung Galaxy S6, Samsung Galaxy S6 Edge, and Samsung Galaxy S6 Edge+ are Android smartphones manufactured and marketed by Samsung Electronics.  The S6 line serves as a successor to the Galaxy S5.  The S6 and S6 Edge smartphones were officially unveiled in the first "Samsung Unpacked 2015" event at Mobile World Congress on 1 March 2015, while the bigger S6 Edge+ was officially unveiled together with the Samsung Galaxy Note 5 in the second "Samsung Unpacked 2015" event at New York on 13 August 2015.