In the Al ha'Nissim of Chanukah, it is referred to Matisyahu ben Yochanan Kohen Gadol. And the Mefarshim discuss on who does the title Kohen Gadol go on.
I want to point out 2 things based on the Gemara in Megilah 11a half-way down the Amud:
1. The name mentioned there is Matisyah not Matisyahu.
2. And this Matisyah is a Kohen Gadol.
allen schuldenfrei, baltimore, maryland USA
These are very interesting questions and are discussed to an extent by the Mefarshim.
1. (a) We find quite a number of names for which sometimes a "Vav" is added at the end and sometimes not. Adding or subtracting the Vav does not change the name. For instance Eliyahu Ha'Navi is usually referred to as Eliyahu with a Vav at the end. However, in 5 places in Nach (the first is in Melachim 2:1:3) he is referred to as Eliyah without a Vav at the end. Nevertheless this is clearly one and the same name. (Other examples include: Yeshayahu and Yeshayah, Chizkiyahu and Chizkiyah, Yirmiyahu and Yirmiyah)
(b) In fact in the recitation of Al ha'Nisim on Chanukah, some have the custom to say Matisyah and others have the custom to say Matisyahu. This is mentioned in connection with the Halachah concerning how to write a Get for a man with the name Matisyahu. The Beis Yosef in Even ha-Ezer 129:24 cites authorities who write that one should write it with a Vav. The reason is that since everyone is familiar with this form of the name from mentioning it on Chanukah, one can assume that the person was named Matisyahu. However, the Beis Yosef writes that since in his communities the custom was to say Matisyah on Chanukah without a Vav, it follows that in a Get it should also be written without a Vav. The Be'er Hagolah on Shulchan Aruch 129:24 writes that since the custom in Germany and Poland is to say Matisyahu on Chanukah, it therefore follows that a get should be written with a Vav. However, I am told that the Ben Ish Chai in Baghdad wrote that their custom was not to add a Vav on Chanukah and this is indeed the custom of many Sefaradim to this day.
(c) Concerning your very observant note that the name mentioned in the Gemara is Matisyah, I would point out that it seems that there are variant texts in this Gemara. Please see Maseches Sofrim(which is printed at the back of the Gemara Avodah Zara)chapter 20 Halachah 8. It writes that in the Shemoneh Esreh we thank Hash-m for the wonders that he did "in the days of Matisyahu the son of Yochanan Kohen Gadol". This suggests that the text in Megilah 11a should also be Matisyahu.
[I believe that I have seen that the Sefer Dikdukei Sofrim on Megilah 11a, which cites all the variant readings, quotes a text which has Matisyahu. I do not have a copy of Dikdukei Sofrim at hand. I also found that the text of the Gemara that the Torah Temimah on Vayikra 21:24 cites is Matisyahu].
2. In reference to your second question, this also can be answered on the basis of a different text in this Gemara. This is found in the SMAG (Sefer Mitzvos Gadol) authored by Rabbeinu Moshe mi'Kutzi. At the end of the section on positive commandments he lists 5 Rabbinical commandments of which the last one is Chanukah. His text in our Gemara is "I established for them Shimon the Righteous and Matisyah the son of Yochanan the Kohen Gadol and Chashmonai and his sons." According to this text it appears that Yochanan was the Kohen Gadol and not Matisyahu his son. This is also the text of the Ein Ya'akov here. Kol Tuv,
Dovid Bloom