Also I say fathers because it was all men (or boys) involved. Only Liisachan on Doom9 was involved in creating the original logo.
Lasse Kärkkäinen (FI)
Lasse is the creator of MCF. The project that Matroska was forked from. Although forks are usually not a great idea, there was so many differences between his original format and how we turned it into what is now Matroska that we couldn't continue working on the same project. We agreed to disagree and went on separate ways. But there were no hard feelings, we met on a few occasions after that. He even asked me for a letter recommendation for a job in Finland once.
Frank Klemm (DE)
One of the key difference between MCF and Matroska is the use of EBML. And one of the key feature of EBML is the way header values are coded in an UTF-8 like manner. This was Frank's idea. And it gave a great boost to the format and why going back to MCF was not possible after that.
Frank was one of the developper of MPC (Musepack) codec which combined lossless and lossy audio compression in the same format. People were so happy with his work that there was a crowdfunding (which didn't exist at the time) on Doom9 to buy him a new PC.
Christian HJ Wiesner (DE)
Christian is not a developer. He's not really a technical guy either. But he liked so much what we were doing that he was organizing everything around the project. He was also the first to join me when I created the fork on Sourceforge. He's also the one who organized the crowdfunding for Frank Klemm and delivered him his PC. He also held the matroska.org domain safe for a long time which he then donated to the Matroska non-profit.
John Cannon, Paul Bryson, Jory Stone (USA)
Apart from Frank and I they were the main input to make changes to MCF that ended up as Matroska. IIRC John Cannon was the one to suggest that the Matryoshka name were planning to use was too complicated for USAns and reduce it to Matroska.
Alexander Noe (DE)
Alexander was also developing an AVI muxer and a Matroska muxer at the same time we created libebml/libmatroska. He gave a lot of input on the format and some refinement which helped a lot. He later turned into artificial intelligence, so I guess he's a millionaire now.
Everyone who has dealt with Matroska has been using mkvtoolnix at some point. It's almost entirely done by Moritz. He joined the project a bit later after it was almost stable. At the time he was working on an OGM tool for Linux and got interrested in doing the same for Matroska. It became mkvmerge. Since then he has been the main maintainer of the Matroska libraries and the main Matroska tool. He's also part of the non-profit.
Михаил "Haali" Мацнев (RU)
Mike create the famous Haali DirectShow demuxer based on his own C library. He also worked a lot on the Segment linking, even doing his own version that was easy to use with DirectShow (but not really clean standardwise). Most people have been playing Matroska files using his code for a long time.
Ludovic Vialle / Dan Marlin (FR/US)
Ludovic is the one that got me into this. I was looking for a container to replace AVI and MPEG PS and he pointed me in the MCF direction. He was working on his own DirectShow player at the time and later founded CoreCodec with Dan Marlin. Corecodec has helped a lot in the Matroska development, helping with the website and mailing lists hosting. At some point we also had our own web forum. They also worked a lot on cleaning the specs that are currently on matroska.org. I also worked there for many years and later with Ludovic's other company LevelUp Studios. Ludovic is also part of the Matroska non-profit.
For reference there's also a longer list of people involved on our website. This list also contains a lot of people who helped develop the many softwares you might have used. It should be updated with all the people involved in CELLAR like Dave Rice, Ashley Blewer, Jerome Martinez, Reto Kromer, Michael Bradshaw, Martin Below or Tobias Rapp.