Gemara

Regarding Ben Kamtzar and his colleagues it says "V'Shem Resha'im Yirkav".

Question: What do we learn from this?

Answer (R. Elazar): We do not name people after them.

Question (Ravina - Beraisa): A case occurred, Do'eg ben Yosef lost his father when he was a young child. His mother used to weigh him and give his weight in gold to Hekdesh. When the enemy overpowered, his mother slaughtered him and ate him.

Answer: Indeed, such is the outcome of giving the name of a Rasha!

Bereishis Rabah (49:1) - R. Yitzchak: If one mentions a Rasha without cursing him he transgresses an Aseh - "V'Shem Resha'im Yirkav";

R. Shmuel bar Nachman says, names of Resha'im are like Kelim used for weaving. They are strong while used, but they slacken after use. Similarly, we do not hear people call their children Paro or Sisera or Sancheriv (their names die out).

On Purim, when Rav mentioned Haman he would say 'cursed is Haman and cursed are his sons', to fulfill "V'Shem Resha'im Yirkav".

Rishonim

Rashi (DH d'Lo): One should not give to his son the name of a Rasha.

R. Chananel (DH she'Ein Adam): Someone given such a name will not succeed.

Tosfos (DH d'Lo): One may give a name if it was the name of a Tzadik and of a Rasha.

Piskei Tosfos (Sotah 20): We avoid names of people who sinned constantly. We are not concerned for someone who sinned only once.

Question: According to the opinion (Sanhedrin 94a) that Avraham does not save Yishmael (from a harsh judgment), why were righteous Kohanim Gedolim and Tana'im given this name?

Answer (Ritva DH d'Lo and Tosfos Yeshanim DH Ma'ase): Since Hash-m said that this name should be given to Yishmael we are not concerned. Alternatively, R. Elazar holds like the opinion that Yishmael did Teshuvah (Bava Basra 16b).

Rashi (Mishlei 10:7): "V'Shem Resha'im Yirkav" - people will not want to give such names, therefore the name will rot.

Acharonim

Maharsha (Ta'anis 28a DH Hu Omer): It is forbidden to call someone by a Rasha's name.

Question: Why don't the Poskim bring this Isur?

Answer (Si'ach ha'Sadeh p. 44b) Question: What was the Gemara's question from Do'eg ben Yosef? Perhaps it was improper for his father to gave him this name. If we infer his father was a Tzadik (from his mother's practice to give his weight in gold to Hekdesh), the Gemara's answer (Indeed, such is the outcome...) does not explain why his father gave him this name!

Answer: The Poskim hold that it is not an Isur. Rather, it is only Midas Chasidus. "V'Shem Resha'im Yirkav" is not a command. It is a curse that people will not be called by that name (Bereishis Rabah 49:1).

Question: We find Tzadikim that used names of the Meraglim, i.e. Shamu'a and Shofat!

Answer #1 (Pnei Yehoshua Kesuvos 104b DH Shnei Dayanei): We attribute their evil to the name 'Meraglim', not to their individual names. Alternatively, it is forbidden only regarding a name which itself suggests evil, e.g. Do'eg (Hash-m 'worried' lest he become evil - Sanhedrin 96b). Perhaps regarding a typical name we may assume that there were Tzadikim of that name before the Rasha. However, Tosfos asked why a Tzadik was called Avshalom. This shows that he disagrees with the latter two answers.

Answer #2 (Divrei Yakov, cited in Shmiras ha'Guf veha'Nefesh 154:1): We are concerned only for someone who was a Rasha from the beginning.

Chasam Sofer (Parashas Korach DH Korach ben Yitzhar): It is difficult to understand why a righteous Levi called his son by in the name of a Rasha (Korach was a chief of Edom - Bereishis 36:16). Perhaps the verse traces his lineage to Levi to teach that in spite of three ancestors who were Tzadikim, his name helped cause him to be a Rasha.

Shmiras ha'Guf veha'Nefesh (ibid.): Mishneh Halachos says that the Rambam permits to call a child by the name of one's father even if he was a Rasha, but one should also intend for a Tzadik of that name.

Chasam Sofer (YD 2:25): Giving the name of a Rasha is an Isur. We must be even more stringent not to give the name of someone who died a premature or tragic death, for this is dangerous. It suffices to make a minor change; this is why people spell 'Akiva' with a 'Hei' at the end; R. Akiva's name ended with 'Aleph'. This is alluded to by the last letters of the verse "Or Zaru'a la'Tzadik ul'Yishrei Lev Simchah".

Igros Moshe (YD 2:122): Alternatively, one may add a second name.