Tsar/czar and kaiser are derived from caesar.

I'm going to assume that 'king' probably does in some tortuous way.

For the curious:

The second incident occurred in 44 BC. One day in January, the tribunes Gaius Epidius Marullus and Lucius Caesetius Flavus discovered a diadem on the head of the statue of Caesar on the Rostra in the Roman Forum.[5] According to Suetonius, the tribunes ordered the wreath be removed as it was a symbol of Jupiter and royalty.[7] Nobody knew who had placed the diadem, but Caesar suspected that the tribunes had arranged for it to appear so that they could have the honour of removing it.[5] Matters escalated shortly after on the 26th, when Caesar was riding on horseback to Rome on the Appian Way.[8] A few members of the crowd greeted him as rex ("king"), to which Caesar replied, "I am not Rex, but Caesar" ("Non sum Rex, sed Caesar").[9] This was wordplay; Rex was a Latin title meaning ‘king’. Marullus and Flavus, the aforementioned tribunes, were not amused, and ordered the man who first cried "rex" arrested. In a later Senate meeting, Caesar accused the tribunes of attempting to create opposition to him, and had them removed from office and membership in the Senate.[8] The Roman plebs took their tribunes seriously as the representatives of the common people; Caesar's actions against the tribunes put him on the wrong side of public opinion.[10]

https://en.wikipedia.org/wiki/Assassination_of_Julius_Caesar