Some Weimar politicians:
Walther Rathenau, perhaps best known for his diplomatic successes which provided Germany room to maneuver after WWI. Some of them in the medium term proved popular even on the far right. Still a target for antisemitic and nationalistic hate he was murdered by Organisation Consul, a far right terror organisation of Freikorps origin. His death threw German foreign politics into a bit of a chaos until Stresemann took over. I doubt he could have prevented the Ruhr occupation, but maybe the entire conflict could have been resolved better with him around. He was internationally well connected and experienced, thus could at least have avoided some of the blunders Stresemann made while he learned to be a foreign minister. As an industrialist, part of the early wartime economic planning and post war rebuilding efforts he also had some interesting ideas about economic policy. On the other hand his death prompted some laws that strengthened the republics position against far-right extremism and their lack too could be ... interesting.
Matthias Erzberger is the other prominent victim of the OC. As minister of finances he basically developed the modern German tax system within one year. He also was a huge target for the right for his attempts to stabilize public finances and for signing the armistice and had stepped down in 1920, nine month before his murder. But with inflation starting to really take off it is well possible that he would have been called back to force through more unpopular, but effective reforms had he survived.
Hugo Stinnes was more successful as industrialist than as politician, but his influence can not be overstated. Time magazine called him the new emperor of Germany, a local saying at the Ruhr equals him to god even today ("Das walte Hugo"). After WW1 he negotiated with the unions the Stinnes-Legien agreement, which legitimated the unions and gave the industrialists some stability at least in relation to their workers. He also was a key figure of the MICUM negotiations which ultimately led to an end of the Ruhr occupation. Personally he managed to greatly expand his business empire in the aftermath of the war despite losing signifcant parts of his pre-war empire and held shares of more than 4500 firms at his death. His death could have been avoided, had his physician simply followed Stinnes requests. Politically he is a man of contradictions, being accused of socialism and exploiting the workers at the same time, condemning the Kapp putsch while providing Kapp with a comfortable exile and financing some of the right wing idiots, being largely pacifist while favouring east expansion, naming ships after both union boss Legien and nutjob general Luddendorff and so on. Much of the contradictions can be explained by his total focus on economic policy and his personal business interests to the exclusion of anything else. After his untimely death his heirs were unable to keep the empire together. Some of those ending in control were early financers of the extreme right with whom Stinnes had clashed over economic policy. Stinnes was not above pacting with the far right (one of his major investments actually was the Hugenberg media company), but just on economic policies he would not have pacted with the nazis from the beginning. His continued control over a significant part of the German industry, his international business cooperations and his sheer ability would also have a noticable effect on the great depression in Germany.
And finally Carl Legien, the leader of the unions for the Stinnes-Legien agreement mentioned above. He is also credited with organising the general strikes that brought down Kapp. He was offered the job of chancellor in 1920, but declined and died rather suddenly the same year aged 59. He also was an early supporter of the republic, positioning himself against a German soviet republic. Widely respected among workers, politicians and industrialists alike, at the time of his death he was the leader of the largest, arguably most powerful union organisation of the world. His replacement could not prevent a softening of some accomplishments in the wake of hyperinflation, in the late 20s had to accept a communist split (to be fair one mandated in Moscow) of the unions and acted very cautious in the 30s, going as far as publically distancing the ADGB from the SPD in a lukewarm attempt to reach an accomodation with the NSDAP.
