Robert Bruce a.k.a Robert de Brus (c 1220s - 31 March 1295), 5th Lord of Annandale, was a feudal lord in Scotland and Northern England during prelude stages of Wars of Scottish Independence, a regent of Scotland in mid-13th century and finally a leading contender (“competitor”) to be the King of Scotland in 1290-92.

He was son of Robert Bruce, 4th Lord of Annandale and Isobel of Huntingdon, daughter of David of Scotland, 8th Earl of Huntingdon.

He descended from royal lineage that would give him and his family a claim to the Crown of Scotland. (In 1306, long after his death, his grandson Robert the Bruce eventually succeeded in becoming the king of Scotland.)

His father's ancestry was of Anglo-Norman stock, the feudal family having come to southern Scotland sometime during reigns of sons of Saint Margaret of Scotland. They held a remarkable barony in the English borderzone, as well as lands in northern England.

He succeeded in having the young widowed Marjorie of Carrick, heiress of that earldom, married to his son, another Robert Bruce in 1271. She was the daughter of Neil, 2nd Earl of Carrick, and his heiress. Carrick was a Gaelic Earldom in Southern Scotland. Its territories contained much of today Ayrshire and Dumfriesshire. The couple held at least Turnberry Castle and Lochmaben. Marriage with Marjorie made the younger Robert an Earl, as was the custom of that time.

Robert Bruce was Regent of Scotland sometime during minority of his second cousin King Alexander III of Scotland (1241-1286) and was occasionally recognized as a Tanist of the Scottish Throne. He was the closest surviving male relative to the king: Margaret of Huntingdon's issue were all females up until birth of Hugh Balliol sometime in the 1260s. When Alexander yet was childless, he was officially named as heir-presumptive, but never gained the throne as Alexander later fathered three children. The succession in the main line of the House of Dunkeld became highly precarious when towards the end of Alexander's reign, all three of his children died within a few years. The middle-aged Alexander III induced in 1284 the Estates to recognize as his heir-presumptive his granddaughter Margaret, called the "Maid of Norway", his only surviving descendant. The need for a male heir led Alexander to contract a second marriage to Yolande de Dreux on November 1, 1285. All this was eventually in vain. Alexander died suddenly, in a fall from his horse, when only 45 years old, in 1286. His death ushered in a time of political upheaval for Scotland. His three-year old granddaughter Margaret, who lived in Norway, was recognized as his heir. However, the then 7-year old queen Margaret of Scotland herself died too, travelling towards her kingdom, on the Orkney Islands around September 26, 1290. With her death, the main royal line came to an end and thirteen claimants asserted their rights to the Scottish Throne.

After this extinction of the senior line of the Scottish royal house (the line of William I of Scotland) David of Huntingdon's descendants were the primary candidates for the throne. The two most notable claimants to the throne, John Balliol and Robert himself (grandfather of another Robert Bruce) represented descent through David's daughters Margaret and Isobel respectively.

Robert Bruce pleaded tanistry and proximity of blood in the succession dispute. He descended from the second daughter of David of Huntingdon, whereas John Balliol descended from the eldest, and thus had the right of primogeniture. However, Robert was a second cousin of kings of Scotland and descended in 4th generation from King David I of Scotland, whereas John Balliol was a third cousin of kings and descended in 5th generation from King David I, the most recent common ancestor who had been Scottish king. The ensuing 'Great Cause' was concluded in 1292. It gave the Crown of Scotland to his family' great rival, John Balliol, instead. The events took place as follows:

Soon after the death of young queen Margaret, fearing civil war between the Bruce and Balliol families and their supporters, the Guardians of Scotland asked the kingdom's southern neighbor, Edward I of England to arbitrate among the claimants in order to avoid civil war. Edward I saw this as the opportunity he had long been waiting for to conquer Scotland as he had conquered Wales and rule over all the British Isles.

Arbitration processed slowly. After initial solutions which left two contenders, on August 3, 1391 Edward asked both Balliol and Bruce to choose forty arbiters while he himself chose twenty-four, to decide the case. There was then an adjournment until June 1292. Upon reconvening, the 104 arbiters wouldn't make a firm decision on the claimants. There was another recess until October 10, 1292, and at this time Edward got the arbiters to agree that as Lord Paramount of Scotland, he had the right to grant the kingship of Scotland as he would an earldom or barony. He chose Balliol on November 17, 1292 and on November 30, John Balliol was crowned as King of Scots at Scone Abbey. On December 26, at Newcastle upon Tyne, King John swore homage to Edward I for the kingdom of Scotland. Edward soon made it clear that he regarded the country as his vassal state. The Bruce family thus lost what they regarded as their rightful place on the Scottish throne.

(Edward I decided in favor of the senior legitimate heir by primogeniture, John Balliol; however, in 1306, the crown was assumed by a grandson of the Robert himself, who became King Robert I.)

Robert's important daughter-in-law Countess Marjorie died in 1292, and on the day of her death his son transferred Carrick to his eldest grandson, the future Robert I of Scotland thus making the boy the Earl of Carrick.

Soon afterwards, Robert himself (Robert Bruce, 5th Lord of Annandale) resigned the lordship of Annandale to his son, the former Earl of Carrick. And also his claim to crown, in order to prevent it from extinguishing.

He was married, firstly, Isabella de Clare, daughter of Gilbert de Clare, 5th Earl of Hertford and Lady Isabella Marshal, on 12 May 1240. After Isabella’s death in 1254, he married, secondly, Christina de Ireby, daughter of Sir William de Ireby.