Count Walter Leslie, (1606-1667), soldier, diplomat and ambassador, was born in 1606 in Aberdeenshire, the second son of John Leslie of Balquhain (? -1622), and his third wife, Jean, daughter of Sir Alexander Erskine of Gogar. By 1624, he had escaped the financial troubles of the family and was fighting in the service of the United Provinces. In 1628 he was at Stralsund, on the Baltic, and by 1630 was serving on the side of the Spanish Habsburgs in the War of the Mantuan Succession (1628-31). By 1631, Leslie had moved northwards again, to help the Imperialist attempt to repel the Swedish under Gustav Adolph. On 8 August 1632, having joined the multi-national regiment of Count Adam Tr¹ka, he fought at Freistadt, but was captured with fellow Scot John Gordon. As prisoners, they appear to have received the admiration and compliments of the Swedes for their prowess.
The entrepreneurial Leslie quickly acquired prestige in the Imperial army following his release. Later in 1632, he was given command of a thousand dragoons at Gordon's garrison at Eger in Bohemia (Cheb, Czech Republic), and was based there until 1634. Meanwhile, his presbyterianism did not prevent him from securing promotion to second in charge of the regiment. By 1633 he had established contacts that were to lead to his involvement in the plot to dismiss, 'dead or alive,' the obscurely-motivated Imperialist General, Albrecht von Wallenstein and his last allies, who included Adam Tr¹ka. On 18 February 1634, the plot received the consent of Ferdinand II, and the General had made a disastrous attempt from his winter quarters at Pilsen (Plzen) to persuade his lower officers to maintain their loyalty. He was thus forced to make a journey via Eger, arriving there in the afternoon of 25 February, on his way towards a presumed escape to Saxony.
It was Gordon and Leslie, along with the Irishman Walter Butler, another regimental commander, who were instrumental in deciding the final course of events. All appear to have been trusted by Wallenstein to the last since Leslie had been sent to meet him the day before, in the apparent belief that the Scot could still be counted on. Again, in the morning of the fateful day, the loyal Count Ilow had tried to win Leslie, Gordon and Butler over from their unquestioning allegiance to the Emperor.
Wallenstein had apparently been feeling ill and had retired to his bedroom in the former burgomaster's house, while his four remaining advisers, including Ilow, accepted an invitation from Leslie and Gordon to a feast at the nearby castle. While all joined to make toasts to the absent generalissimo, the drawbridge was closed and a signal came from Leslie for a group of Scottish and Irish dragoons to enter, slaying all four as the others watched, proclaiming `Vivat Ferdinandus, Vivat Domus Austria!' An Irishman, Deveroux went with a small group to Wallenstein's residence, finding him defenceless in his bed-clothes, and killed him. It remains uncertain if the colourful, gruesome legend that the General's corpse was then conveyed through the streets of the town in a manure-cart to he dumped with the other bodies is entirely accurate.
Nevertheless, the conspiracy demonstrated to surprised contemporaries the hitherto-unknown influence of Leslie within the Imperial army. After arriving in Vienna on 6 March, he was awarded the post of Imperial Chamberlain and on 16 April the command of two regiments. Earning ever more favour, he soon converted to Catholicism. Nevertheless, his subsequent military career was sporadic and frequently disastrous, and absenteeism led to him being deprived of his last regiment in 1642. His main prize at Eger had in fact proved to be the award of Tr¹ka's grand estate, at Neustadt (Nov¾ Mesto-nad-MetujÍ, Czech Republic), a prize which far outweighed the significance of his involvement. Through baroque-inspired renovations there and particularly following his acquisition of the title of Reichsgraf on 26 June 1637, he expressed his noble claims by various means in order to increase his courtly prestige.
His post-1636 diplomatic friendships with ambassadors from the British Isles, Lord Basil Feilding, Sir Thomas Roe, Thomas Howard of Arundel and Sir Heneage Finch, were to lead to co-operation, firstly in bringing about the release of Prince Rupert of the Palatinate from prison in 1638 and in attempts at a restoration of the privileges of the Palatinate to Charles Louis, fellow son of the exiled royal family, during negotiations at Ratisbon (Regensburg) in 1636 and again in 1640-2. In 1642, as his reward for these services, Leslie requested to have his elder brother William (?-1671) bestowed instead, with a position on Charles I's Privy Council. His power in Imperial affairs further increased after marriage to Anna Francesca Dietrichstein, daughter of Maximilian, Prince of Dietrichstein, which seems to have occurred either in 1640 or 1647. He later also gained possession of Wallenstein's palace in Prague, but it was his acquisition of the castle of Oberpettau (Ptuj, Slovenia) from the Jesuits at auction in Zagreb in 1656, which signalled his new role in the south-eastern Habsburg lands.
Sent to negotiate loans in Italy, a trip which included a meeting with Pope Innocent X in Rome on 21 April 1645, by 5 January 1650, he had become warden of the Slavonian marches and on 23 August was appointed as Field Marshall and General on the so-called 'Croatian-Slavonian military frontier.' By 1657, already an adviser to the Imperial Privy Council, he was appointed Vice-President of the War Council. Five years later, he sent back money again to another brother Alexander (?-1677), and in his will of 27 May 1663, not only left money for him and two other brothers still in Aberdeenshire, but arranged to have his Styrian and Bohemian estates fall to his nephew, Alexander's son James. Hence, James and another nephew accompanied him, following his award of the Order of the Golden Fleece on 6 May 1665, on his last, lavish embassy, to Constantinople. He died on 3 March 1667 and was buried in the Scottish Benedictine Abbey in Vienna.