Cyrillic Capital Letter Io
HTML Entity Browser Test:

U+0401 is the Unicode hex value of the character Cyrillic Capital Letter Io, which is categorized as "uppercase letter" in the Unicode 6.0 character table.

In addition, U+0401 is a composite character comprising of one or more other Unicode characters modified or combined.

Unicode Character Information
Unicode Hex U+0401
General Category Uppercase Letter [Code: Lu]
Canonical Combining Class 0
Bidirectional Category L
Decomposition Mapping 0415 0308
Mirrored N
Lowercase Version U+0451
Unicode Character Encodings
Cyrillic Capital Letter Io HTML Entity Ё (decimal entity), Ё (hex entity)
Windows Key Code Alt 1025 or Alt +04011
Programming Source Code Encodings Python hex: u"\u0401", Hex for C++ and Java: "\u0401"
UTF-8 Hexadecimal Encoding 0xD081
1 To type a Unicode symbol in Windows, hold down the ALT key and enter the decimal or hexadecimal code provided using the numeric keypad. The decimal alt code (Alt 1025) will only work on computers with support for this Unicode character in the active code page. The hexadecimal alt code (Alt +0401) will work for all Unicode characters provided Hex input from the numeric keypad is enabled.
* If the Cyrillic Capital Letter Io character does not display correctly in your browser, you may not have a Unicode font on your system that supports this particular symbol.