This is a difficult question to not politicize in the sense that the sources are few. Perhaps Seljuk was simply introduced to the religion of Islam once he moved his tribe closer to Transoxiana and he found it more appealing and began to practice it. It is believed that Seljuk and more particularly his father, Duqaq, were already practicing a either the Jewish faith, or the Nestorian Christian faith. There are a few elements that point to this: Seljuk is known to have personally served in the Khazar army, who were known for their Jewish elites, but the real indicator here are the names of his sons, which all bear names that derive from the Old Testament, such as Israel, Moses, Michael, Joseph and David. Now, keep in mind that as the Seljuk dynasty progresses, they typically either have traditional Turkish names or they just have Arabic names.

The Samanid dynasty which was ruling in Iran at the time did use a tactic of converting the barbarous nomads which they found to be a nuisance, and they thought that introducing Islam to them was a great way of taming and educating them. It is entirely possible that it was introduced to Seljuk in this manner as well. We know that this was a successful tactic for the Samanids as the Kara-Khanids did convert in large amounts to Islam during the 11th century.

Now, regardless of whether Seljuk was very religious or not is irrelevant at this point because from a political standpoint becoming Muslim would have been very advantageous. In the 11th century and even the 12th century as a matter of fact, the Islamic world was becoming more and more Muslim. What I mean by this is that a large number of people stretching from Iran to the Levant were embracing Islam as their religion, and this isn’t only the pagan people, it is also the Christians and the Jews. With the population of these lands becoming more Muslim, I’m sure you can see why it would be beneficial to be Muslim as a ruler.

If you want to read more about the rise of House Seljuk, I wrote about it here.

After Seljuk died, his grandson Tughril took over the clan, and once he and his brother Chagri took control of a large chunk of Khorasan there was great fear in the hearts of the people of the region as the Shamanistic infidel nomads had now come to rule over a sedentary society. However, Tughril, did something I find to be absolutely brilliant; he announced himself as a Muslim man ready to not only fight for Islam, but also protect the Arabo-Persian culture of the region which further solidified his position politically.

The one thing I haven’t mentioned (and I did this on purpose), is the fact that the Seljuks not only converted to Islam, but more specifically Sunni Islam. The reason this is so important is because most of the people living under what will be the Great Seljuk Empire are followers of the Sunni faith, give or take a couple of regions that are a Shia majority. But before the Seljuks spearhead their forces into the middle-east they had to deal with the Buyid Emirates which is a Shia dynasty. The Buyids were essentially keeping the Abassid Caliph in Baghdad on lockdown; not to the literal sense, but he was very limited to his location so by 1055, when Tughril expelled the Buyids the Caliph and the people saw the Seljuks as champions of the Sunni. Many scholars believed this to be the revival of the Caliphate but the Seljuks were not without their critics as they believed them to be too cruel and not real Muslims because they often continued to practice their Shamanistic ways. This doesn’t come as a surprise because the Turks were a warlike people and grew up in a very harsh environment, this made them especially cruel and accounts are provided to us about their militant administration.

In short, it can be said that Seljuk and his descendants may or may not have been devout Muslims, or perhaps it was all “propaganda” to further solidify their stance as leaders of the region. But the fact that the Kara-Khanids, another Turkic confederation had also adopted Islam, it is fair to say that it may have also been appealing to the Turkic people rather than just a political tool. This is still a subject of debate among scholars.

The Great Seljuk Empire, A. C.S. Peacock (The Edinburgh History of the Islamic Empires)

The Barbarians of Asia, Stuart Legg

The Empires of the Steppes, Rene Grousset translated by Naomi Walford

Manzikert 1071, David Nicolle