U.S. anthropologist and folklorist Ruth Benedict, 1887–1948
Ruth is an English, German, Dutch, Spanish, and Scandinavian name derived from the Hebrew Re’ut (friend), which later morphed into Rut (pronounced with a long U, not like the English word “rut”). Most people are familiar with it as the title character of the Book of Ruth. She left her homeland Moab behind to follow her mother-in-law Naomi back to Israel after a famine, and became King David’s great-grandma.
On the second day of Shavuot, this short book of the Bible is read, and many conversion certificates quote the moving words Ruth tells Naomi:
“Do not entreat me to leave you, and to return from following after you; for where you go, I will go, and where you lodge, I will lodge; your people will be my people, and your God my God; where you die, I will die, and there I will be buried; the Lord do so to me, and more, if anything but death part you and me.”
Latvian lawyer, writer, and politician Ruta Šaca-Marjaša (1927–2016)
Though the name has long been common in the Jewish world, it didn’t come into widespread usage in the Christian world till the Protestant Reformation. Ruth received a big boost of popularity several centuries later, from U.S. President Grover Cleveland’s firstborn child, born in 1891. She was born between his two non-consecutive terms, and sadly died of diphtheria in 1904.
Ruth was #93 in the U.S. when name popularity records began in 1880, and it jumped from #19 to #5 after the birth of Ruth Cleveland. In 1893, it was #3. The next two years, Ruth was #6, and it remained at #5 until 1907. It then was #4 for two years, then back to #5 again till 1922.
The name remained in the Top 10 till 1930, and was Top 20 till 1937. Ruth left the Top 50 in 1951, and left the Top 100 in 1962. In 2018, it was #265.
Ruth Cleveland
Other forms of the name include:
1. Ruta is Polish, Ukrainian, and Maori. The alternate form Rūta is Latvian and Lithuanian.
2. Rute is Portuguese.
3. Ruut is Finnish and Estonian.
4. Rut is Hebrew, Spanish, Icelandic, Scandinavian, Sorbian, Italian, Maltese, Indonesian, Afrikaans, and German. The alternate form Rút is Czech and Slovak.
5. Ruf is Russian. I’ve never been a fan of Russian names where TH is replaced by F in the middle of the name. It just sounds ugly to my ears.
6. Rutt is Estonian.
7. Hrut is Armenian.
8. Hirut is Amharic.
9. Luka is Hawaiian, and not to be confused with the entirely separate name with the same spelling which is several languages’ form of Luke.
10. Luti is Nyakyusa, a language spoken in Tanzania and Malawi.
11. Rutu is Maori and Yoruba.
Onomastics Outside the Box 
I’m also not a fan of Russian names with f instead of th.
Ruta is indeed the proper, traditional and linguistically correct Polish form of Ruth, since typically and traditionally all feminine names in Polish (with a few very rare exceptions) end with an A and for many years it would even have been difficult to register a baby girl with a non-A ending name because among the naming rules there was such that a name should indicate the gender of the bearer. But, actually, despite that, Rut is also in use and is one of those exceptions that were allowed with no problem despite not ending with an a. For example the Biblical Ruth is called pretty much exclusively Rut these days in Polish, rather than Ruta. Despite both Ruta and Rut are rare names here, I happen to know two Polish Ruts, one of them in her 90’s or so and the other would now perhaps be in her early 30’s and is of Jewish descent, while I can’t think of a single Ruta that I would ever have even just heard of.