Murong De (Chinese: 慕容德; 336–405), name changed in 400 to Murong Beide (慕容備德), courtesy name Xuanming (玄明), also known by his posthumous name as the Emperor Xianwu of Southern Yan (南燕獻武帝), was the founding emperor of the Xianbei-led Southern Yan dynasty of China. He was the son of Former Yan's founding prince Murong Huang (Prince Wenming) and younger brother to both Former Yan emperor Murong Jun (Emperor Jingzhao) and Later Yan emperor Murong Chui (Emperor Wucheng), and therefore was an imperial prince and general during the times of both states. After Murong Chui's son Murong Bao lost most of the Later Yan's territory to the Northern Wei dynasty, Murong De took troops under his own command south and established Southern Yan, which secured modern Shandong, but failed to expand further, and was destroyed by the Eastern Jin dynasty after Murong De's death and succession by his nephew Murong Chao. The Book of Jin described Murong De as having a stalwart and extraordinary appearance and was about two metres tall.

Murong De was born in 336 to Murong Huang and his concubine Consort Gongsun, who had previously given birth to his older brother Murong Na (慕容納). At that time, Murong Huang was the Duke of Liaodong and a vassal of Jin, although in 337 he claimed for himself the title of Prince of Yan (as Prince Wenming). As this was without Jin authorization (although Emperor Cheng of Jin would retroactively recognize this in 341 by creating him that title), this generally was considered the founding of the independent Former Yan state. When he was young, he was regarded as studious, handsome, and talented.

In 354, after Murong De's older brother Murong Jun (Emperor Jingzhao) formally broke from Jin and claimed imperial title, he created Murong De the Duke of Liang. Sometime after Murong Jun died in 360 and was succeeded by his son Murong Wei, Murong De was created the Prince of Fanyang. By 368, he was the mayor of the capital Yecheng (鄴城, in modern Handan, Hebei) when four dukes of the rival Former Qin rebelled against Former Qin's emperor Fu Jiān. Murong De suggested to the regent, his uncle Murong Ping, that Former Yan activate its troops to aid one of them, Fu Sou (苻廋) the Duke of Wei and further take the chance to conquer Former Qin, but his strategy was rejected by Murong Ping.

In 369, when the Jin general Huan Wen launched a major attack on Former Yan, seeking to destroy it, Huan was initially successful and reached Yecheng's vicinity. Murong De's older brother Murong Chui volunteered to make one last attempt against Huan, and Murong De was a general under his command. Together, they dealt Huan a major defeat, forcing Huan to abandon his campaign. However, later that year, Murong Chui, under suspicion by Murong Ping and Murong Wei's mother Empress Dowager Kezuhun, was forced to flee to Former Qin, and because of the close relationship Murong De had with Murong Chui, Murong De was removed from his post as the mayor of Yecheng. After Former Qin conquered Former Yan in 370, Murong De, as other princes of the Murong clan did, surrendered to Former Qin forces.

Fu Jiān made most Former Yan princes commandery governors in his empire, and both Murong De and his brother Murong Na were commissioned as such, but Murong Na was soon removed from his office, and both Murong Na and their mother Consort Gongsun relocated to Murong De's post at Zhangye Commandery (張掖, roughly modern Zhangye, Gansu). Around or in 383, when Fu Jiān prepared a campaign to destroy Jin and unite China, Murong De and his troops were mobilized, and he left his own sons, Murong Na, and Consort Gongsun in Zhangye; before leaving, he gave his mother a golden knife as a sign of his devotion.

After Fu Jiān's defeat by Jin forces at the Battle of Fei River, Murong De first tried to persuade Murong Chui, to whose camp Fu Jiān had fled, to kill Fu Jiān and start a rebellion to rebuild Yan. When Murong Chui refused, citing Fu Jiān's kindness to him, Murong De then tried to persuade Murong Wei to do so, but Murong Wei also refused.

In spring 384, however, Murong Chui did start a rebellion near Luoyang, and after he claimed the title of Prince of Yan, thus establishing Later Yan, he created Murong De his old title of Prince of Fanyang. When the news reached Zhangye, the commandery governor Fu Chang (苻昌) arrested and executed Murong Na and all of Murong De's sons (and presumably their mother(s)). Consort Gongsun was spared because of her old age, while Murong Na's wife Lady Duan, who was then pregnant, was imprisoned to await for execution after she gave birth. Consort Gongsun and Lady Duan, however, were rescued by Murong De's former subordinate Huyan Ping (呼延平), who escorted them to the Qiang tribes.

During Murong Chui's reign, Murong De served as a chief official and general, and Murong Chui often listened to his advice. For the first several years of Later Yan's existence, he often carried out campaigns to secure areas that were being held by semi-independent warlords. In particular, around the new year 387, he, assisted by his nephew Murong Long, was successful in defeating the Jin vassal Wen Xiang (溫詳) and the Jin rebel Zhang Yuan (張願), taking the territory near the Yellow River.