[1] As a negotiator he was very useful to Gustavus Adolphus because of his ability to "drink immeasurably and preserve his understanding to the last", and he also won fame on the field of battle.
Ruthven was one of four Scottish colonels to be knighted by Gustav II Adolf of Sweden in 1627, the others being Alexander Leslie, David Drummond and John Hepburn.
The following year Ruthven campaigned along the Danube where he captured a number of Bavarian Horse outside Erbach which earned him his promotion to lieutenant general.
He was given a large share of the credit for the routing of the Saxon general, Wolfgang Baudissin at Dömitz, where some 2500 of the prisoners he took were pressed into the Swedish army.
[4] Although Ruthven remained on the Swedish pay-roll for another year he travelled home via France where he claimed he was offered a field-marshal's baton by Louis XIII.
After the Truce of Berwick was agreed, Ruthven was allowed to garrison the castle for the king and he defended it throughout 1640, becoming desperately ill after his provisions ran out.
When the English Civil War broke out that year, Ruthven joined Charles at Shrewsbury with some 29 other Scottish veteran officers and after Henrietta Maria's intervention with the king.
Using the social capital he had built up in Sweden over the years, Ruthven entered into negotiations with Queen Christina and managed to raise an officer cadre, money and guns for delivery to Royalists in Scotland and Ireland.
To his surviving wife, Clara Berner and their son Patrick, he donated Ljungbyholm in Kalmar Län (Sweden) and Sackendorf (Mecklenburg).
Clara and his daughter-in-law Anna Klence fought protracted disputes over the Småland lands, even until 1669, and these involved royal intervention.
According to contemporary sources, Ruthven's behavior was consistent with that of a severe alcoholic, and at times he was called "Rothwein" (red wine).
At the time of his resignation as commander in chief in 1644 he is said to have shown clear signs of chronic alcohol damage, and that may have been a factor contributing to his replacement by Prince Rupert of the Rhine.