Crito
The dialogue takes place in Socrates' prison cell, where he awaits execution. He is visited before dawn by his old friend Crito, who has made arrangements to smuggle Socrates out of prison to the safety of exile. Socrates seems quite willing to await his imminent execution, and so Crito presents as many arguments as he can in order to persuade Socrates to escape. On a practical level, Socrates' death will reflect badly on his friends--people will think they did nothing to try to save him. Also, Socrates should not worry about the risk or the financial cost to his friends; these they are willing to pay, and they have also arranged to find Socrates a pleasant life in exile. On a more ethical level, Crito presents two more pressing arguments: first, if he stayed, he would be aiding his enemies in wronging him unjustly, and would thus be acting unjustly himself; and second, that he would be abandoning his sons and leaving them without a father.
Leon of Salamis
In the "Apology", Plato's Socrates argues that he fears committing injustice more than he fears death. In support of that claim, he cites two incidents in which he, at great personal risk, disobeyed unjust commands of the Athenian government. One of those orders was for him to arrest Leon of Salamis and bring him to the Thirty for execution:
When the oligarchy was established, the Thirty summoned me to the Hall, along with four others, and ordered us to bring Leon from Salamis, that he might be executed. They gave many other orders to many people, in order to implicate as many as possible in their [i.e., the Thirty's] guilt. Then I showed again, not in words but in action, that, if it's not crude of me to say so, death is something I couldn't care less about, but that my whole concern is not to do anything unjust or impious. That government, as powerful as it was, did not frighten me into any wrongdoing. When we left the Hall, the other four went to Salamis and brought in Leon, but I went home. I might have been put to death for this, had not the government fallen shortly afterwards. ("Apology" 32c–d)
From these texts, it is clear that Leon of Salamis had an honorable reputation, he was put to death by the Thirty, and his execution was publicly recognized as unjust and unwarranted. But this leaves open the question of who Leon was.