"For He's a Jolly Good Fellow" is an extremely popular nursery rhyme. Actually, "For He's a Jolly Good Fellow" is said to be the second most sung song in the world (English language) (!) Only Happy Birthday To You is more popular.
For He's a Jolly Good Fellow dates back to the 18th century. It was first released in France, with Frech lyrics. In the mid-19th century it became popular in America (and then England), with the English language lyrics that we know today.
For He's a Jolly Good Fellow is a great birthday and party song! Remember that "He" easily can be replaced with "She"! You can also use a person's name instead of "He". For example: For Robert's a Jolly Good Fellow..., or "For Julia's a Jolly Good Fellow..."