How could Hitler have been prevented from coming to power? Or successfully removed?

[MiddleRoad]

Same question as title.

He was the worst person, probably, in history and destroyed not only millions of lives, but a great country (Germany)

[AtorBoltox]

Prevented - if Chancellor Henrich Bruning had not pursued deflationary policies at the height of the great depression. Once fully in power, the only practical way he could have been removed is via a military coup (which was mooted at the height of the Sudeten crisis) or if a lone assassin had succeeded 

[Amenhotep Bakari-Sellers]

The League if Nations Wilson wanted to start we have been successful preventing a third World War since UN, but it still would of been difficult because now every nation has nukes before Hitler there were no nukes

[Lumine]

Among a few other possibilities:

PREVENTED:
Early 1932: Hindenburg does not stand for reelection (Brüning fails to convince him), a replacement pro-democracy candidate wins the Presidential Election and refuses to appoint Hitler as Chancellor.

Mid 1932: Hindenburg wins as in OTL, does not dismiss Brüning in favor of Papen. Prussian coup averted, Braun (SPD) remains in charge in Prussia and provides something of an additional roadblock to dictatorship. Brüning still likely to attempt shenanigans with Hitler, but unlikely that he'd willingly make him Chancellor.

Late 1932-Early 1933: Papen does not persuade Hindenburg to appoint the Hitler/Papen Cabinet. Von Schleicher gets to reap the benefits of partial recovery by remaining Chancellor, establishes a stronger position. Nazi Party fails to avoid bankruptcy and starts to fall apart in incoming elections.

REMOVED:
Mid 1934: After the Marburg Speech, von Papen actually seizes the moment and visits Hindenburg immediately, and persuades him to dismiss Hitler and bring the Reichswehr in. Likely unrest, possible civil war, but still a chance of success.

After that, it has to be a Wehrmacht coup (likely led by Beck) in the 1936-1939 window if any of Hitler's major foreign policy gambles encounters fierce pushback and causes a crisis/early war). Then you enter WW2, and it's one of the many assassination plots still leaving the Nazis in control (Elser in 39', Tresckow in 43') or the actual Valkyrie coup in 44, which, in my personal opinion, was never likely to succeed at taking over even if Hitler himself was removed via assassination.

[NewYorkExpress]

Hindenberg doesn't win in 1925. In my opinion, Hindenberg was always going to appoint Hitler as Chancellor eventually, and it was only his personal dislike from Hitler that prevented it from happening sooner.

[Yeahsayyeah]

Hindenburg not appointing him to the Reichskanzler spot at a point when the support for NSDAP was actually beginning to shrink, surely would have helped. Hindenburg not eroding democratic institutions and coming up with own putsch plans surely would have helped, too.