Tatsunoko Production Co., Ltd. (but generally referred to as Tatsunoko Pro.) is one of the notable and famous Japanese animation studios back during the Golden Age of Anime. Founded in October 19, 1962 by one of the animation pioneers Tatsuo Yoshida (1932-1977) along with his brothers Kenji (b. 1935) and Toyoharu (a.k.a Ippei Kuri, 1940-2023), the studio began to produce anime occupying various genres. The name Tatsunoko even has a double meaning, with tatsu no ko meaning Tatsu's Child (as in Tatsuo's child) and tatsunoko meaning sea-dragon (which is generally referred to a seahorse), hence the logo.
If Toei Animation is regarded as "Japan's Disney," Tatsunoko could be compared to Hanna-Barbera. Over the years, Tatsunoko Pro. has produced many anime, most of which are memorable (especially if you are Japanese). Even countries like France, Italy, and Quebec got a great deal of their stuff, including Yatterman and Hutch the Honeybee. They are also known for making many of the dubbed (Macekre? Bowdlerise? Woolseyism? You decide) anime which were thought as cartoons back then in the US - Speed Racer, Macross, Samurai Pizza Cats, Gatchaman, Superbook, The Littl' Bits, to name a few. They generally produced a lot of stuff during the 70's and 80's, and slowed down during the 90's, in which they focused more on remakes and co-worked with other studios and animated shows for other companies (such as doing most of the heavy lifting for GAINAX on Neon Genesis Evangelion).
Tatsunoko remained in the Yoshida family until 2005, when Kenji Yoshida (president from 1977-87) and Ippei Kuri (president since 1987) resigned as the studio was bought by Takara, which then became a full subsidiary when Takara merged with TOMY. Takara would sell all but 25% of their stock to other companies. Since 2014, Tatsunoko is a subsidiary of the Tokyo-based television network Nippon TV, which owns a majority stake in the studio; TOMY currently owns 20%. Tatsunoko established its own subsidiary, Bakken Record, in 2019.
Tatsunoko Pro. is notable for starting the career of Yoshitaka Amano, who did the character design of Science Ninja Team Gatchaman, Tekkaman The Space Knight (SPACE LANCE version), Neo-Human Casshern (original version), nearly all of the Time Bokan series... wait a minute, did we just mention nearly everyone from Tatsunoko vs. Capcom? Also, many of their employees have gone on to found other Japanese animation studios of today like Studio Pierrot (including Mamoru Oshii), Bee Train, and Production I.G. (which now owns 11.2% of its "parent" company).
They even earned a Shout-Out in an episode of Mad Men as the animation studio contracted to produce an anime based on the Scout's Honor comic strip. Nevertheless, unlike their rivals Toei and TMS, they didn't do a lot of outsourcing work for Western producers.
In recent years, the company has worked on the new Beyblade anime as well as the movie of Hutch the Honeybee. They also released a Live Action Adaptation of Yatterman helmed by cult director Takashi Miike, which like The Great Yokai War was aimed at younger audience than most of his movies and became a great success. They have also faced renewed appreciation in the west due to the appearance of Tatsunoko vs Capcom on the Wii, first only to Japan, and then, with the Updated Rerelease appearing everywhere.
Go visit their Japanese or English sites for full listing of their works. Check out their entry in The Other Wiki too. A near complete list of their credits can be seen here.
Do not confuse with Tatsu no Ko Taro (aka Taro the Dragon Boy), the children's novel by Miyoko Matsutani which was adapted into anime by Tatsunoko's rival, Toei.