Was there any evil tyrant in athens during the 6 - 5th BC ?

The 6th century saw several periods of anarchy (literally: no archons, the nine chief magistrates in the Athenian state in this period), several attempts at constitutional reform (Solon at the beginning of the century, Cleisthenes at the end), several failed attempts to set up a tyranny (e.g. Damasias, Peisistratus twice, Isagoras) and one successful tyranny – that of Peisistratus and his sons, which lasted for a couple of decades (Peisistratus: 546-27 BC, Hippias: 527-10 BC).

P. himself was seen as a good ruler, despite being a ‘tyrant’ (though it’s worth thinking about what this term actually means – there wasn’t an official position called ‘tyrant’). His sons who succeeded him – Hippias and Hipparchus – were also good, at least initially. Then, in 514 BC, one of the sons – Hipparchus – was assassinated. This resulted in the other one – Hippias – becoming much harsher, i.e. more ‘tyrannical’ in the negative sense. That’s your first ‘evil tyrant’. But he only lasted four years. He was booted out in 510 BC.

The Athenians enjoyed democracy for almost the whole of the fifth century. The only time that changed was first when the franchise was massively restricted after the Sicilian Expedition in 413 BC, a period known as the Four Hundred, and second after the final Athenian defeat in the Peloponnesian War when a small group of aristocrats put themselves in charge. These guys were known as the Triakonta, the ‘Thirty’, and while their rule started off okay, it ended up being very harsh and there was a democratic counter-revolution that restored the democracy just over year later.

TL;DR: Yes, a short period of harsh tyranny at the end of the 6th century after the death of Hipparchus (514 BC) and the deposition of Hippias (510 BC) – literally a couple of years – and some short-lived oligarchic governments at the end of the 5th century.