That is a male Veiltail Betta. It is not safe to have any other Betta with him, ever. They would kill each other.
While it depends somewhat on a Betta's personality, there are some options to keep with him.
Nerite snails - these need a pH of 7.0, algae wafers every other day, and a small piece of unflavored cuttlebone as a calcium supplement. They need a tank of 5 gallons or larger.
African Dwarf Frogs - these need at least 2 of their own kind, must be target fed frozen foods with a turkey baster such as brine shrimp and glass worms, and at least a 10 gallon tank for them and the Betta.
Corydoras Catfish - for Dwarf varieties get at least a 15 gallon, for regular sizes get at least a 20 gallon tank. They need to be kept in groups (8 or more of their own kind for the Dwarf varieties, 4 or more for the regularly sized varieties), plus smooth sand substrate and sinking food for omnivores.
Peaceful male Bettas may also tolerate less colorful, non-fin-nipping types of fish such as Black Neon Tetras, Panda Platies, Otocinclus Catfish, etc. in 20 gallon or larger aquariums. Black Neon Tetras need at least 6 of their own kind. Platies need alkaline water and at least 3 of their own kind, and all males if you don't want them to breed. Otos need excellent water quality, tanks set up for at least 6 months, 4 of their own kind, and sinking algae wafers.