What is known about his identity and life, many of them are based on works written in the late period? With the contemporary Byzantine historian Georgios Pachymeres, XIV. Ertuğrul Gazi’s name is not found in the works of Ioannes Kantakuzenos and Nikephoras Gregoras, one of the Byzantine century historians. Again his works XIV. Even though Islamic historians such as Ibn Fazlullah al-Ömerî and İbn Batttata who wrote in the mid-century mentioned about Osman Bey, they do not give any information about Ertuğrul Gazi. Information about him, XV. It takes place in the first Ottoman chronicles that began to be written at the beginning of the century. In many of these sources, it is stated that the father of Osman Bey, the founder of the Ottoman State, was Ertuğrul and Oğuzlar was a member of the Kayı tribe.
The object of Ertuğrul Gazi is taken to Oğuz Han in different ways and even from there to the prophet of Nûh in the mentioned sources written 100-150 years after the establishment. The names of Ertuğrul Gazi’s father were mentioned in two different ways in these sources, almost all of which were buried in the mencibevi information about the first years of the Ottoman Empire. While one of the first Ottoman historians Ahmedî, Enverî and Karamânî Mehmed Pasha wrote that his father was Gündüz Alp, Oruc b. Historians like dil, Âşıkpaşazâde and Neşrî recorded his name as Süleyman Şah. The information given in this second source group seems to be certain today. As a matter of fact, on a coin belonging to Osman Bey, “Osman b. Ertuğrul b. The presence of the phrase “Daytime Alp” has further strengthened this idea.The ancestors of Ertuğrul Gazi, who belonged to Kayılar, one of the five Oghuz tribes who ruled according to the historical memorial, first came to the Ahlat region during the first conquest of Anatolia, and then to the district of Gazâ and Anatolia. They participated in the futuristic movements, then connected to Ahlat orders and fought against Georgians and the Greek Cypriot Empire in their entourage. XIII. At the beginning of the century, they came to Mardin upon the seizure of the Ahlat region of the Mongols after the seizure of Ahlat by the Ayyubids, and they were connected to the Artukoğulları, who were members of the Kayı neck. It is understood that they were staying here for a while, and Gündüz Alp and the Turkmens accompanying them moved to the interiors of Anatolia after the Mongols raided Mardin and its surroundings. Meanwhile, Germiyan residents living in the vicinity of Malatya came to Kütahya region and Kayılar, under the direction of Gündüz Alp, migrated to the west and first settled in Pasmalı plain near Erzurum, Sürmeliçukur. It is understood that, shortly after Kayılar came to Pasinler, Gündüz Alp died and became his son Ertuğrul Gazi.
Again, according to the historical memorial, despite the Mongol attacks being felt in these regions, Ertuğrul Gazi moved to the west with his brother Dündar Bey despite his brother Sungur Tegin and Gündoğdu returning to Ahlat. When he came and stayed near Sivas, he saw that a large Mongolian unit was fighting with the Seljuk army and that the Mongols were about to destroy the Seljuk army. When Ertuğrul Gazi helped the Seljuk army, the course of the war changed and the Seljuks won. Only Neşrî’s CihannümâIt is also said that this war, recorded in ‘, was the Yassicim War (1230) between the Seljuk Sultan Alâeddin Keykubad and Hârizmşahlar. After the war, Alâeddin Keykubad Ertuğrul made Gazi compliments to Gazi for his help, and when he learned that they migrated to live in the Seljuk country, he gave him Karacadağ and his surroundings (1230).
Ertuğrul Gazi remained in Karacadağ for a while, then sent his son Savcı Bey (Saru Yacht) to Sultan Alaeddin Keykubad and asked him for a new home. According to the Ottoman sources, after getting the necessary permission from the sultan, he moved to the Byzantine borders in order to obtain more fertile soil and settled in the Lower Sakarya basin around Söğüt. Here, he started to organize raids against the towns and villages in the Byzantine borders. Meanwhile, Alâeddin Keykubad organized an expedition to the Byzantine lands in order to obey the western borders of his country. Ertuğrul Bey came here with his entourage and joined the sultan when the army, which moved from Konya in 1231, came to Sultanöyöy (Eskişehir). The Seljuk army won the battle between the Seljuk army and Nikaia (Iznik) Greek Emperor Teodoros Laskaris in the place called Ermeniderbendi between today’s Pazaryeri and Bozüyük, as a result of the successful struggle of the raider cavalry under the command of Ertugrul Bey. When this news reached Alâeddin Keykubad in Sultanöyük, the sultan was very happy and gave Ertuğrul Gazi to Eskişehir and its surroundings.
After this victory, Alaeddin Keykubad besieged Karahisar (Karacahisar), one of the important centers of the region, but at that time, when he received the news that the Mongols had entered Anatolia, he had to return to the city’s occupation by Ertuğrul Gazi. Ertuğrul Gazi and his accompanying Turkmen gentlemen captured Karacahisar as a result of a long struggle (629 / 1231-32).They shared the rest of the booty among the veterans. After Ertuğrul Gazi captured Karacahisar Castle, he walked over Söğüt and dominated this place, the first capital city of the Ottoman Principality. As a result of his successes, Seljuk sultan gave Söğüt and his surroundings to him as a dorm.After settling around Ertuğrul GaziSöğüt and his surroundings, he continued his struggle with the other extreme gentlemen of the Byza ntine border and also tried to establish friendship with neighboring Greek gentlemen (tekfurlar). Ertuğrul Gazi was also in friendly relations with the sons of Hüsâmeddin Çoban, who was from the Kayı Turks like himself and the Kastamonu tip of the Seljuks. In this way, Ertuğrul Gazi, who spent the winters in Söğüt and the summers in the Domaniç plateaus, occasionally raided the regions in the Byzantine borders. Experienced extremists such as Akça Koca, Samsa Sergeant, Kara Tegin, Aykut Alp and Konuralp gathered around him during his raids against Byzantium. Thus, the Kayı tribe, which settled in Söğüt, became stronger with each passing day. According to the rumors in the Ottoman sources, Ertuğrul Gazi, who continued his activities as a lord of the Anatolian Seljuks in Western Anatolia, came to the Byzantine borders after the miser event, the Seljuk Sultan III. Giyâseddin greeted Keyhusrev and reported loyalty and presented gifts (1279). It is understood that after this date, Ertuğrul Gazi was very old and left the administration of the Kayı tribe to his son Osman Bey. Probably died shortly after this deadline even though he was over ninety years old (680 / 1281-82). The date of death is given in 1288 or 1289. Tomb Bilecik province Söğüt district 1 km. east of Söğüt-Bilecik road. Those who belonged to the Kayı tribe and especially the Karakeçili tribe Ertuğrul Gazi after his death, made his tomb a spiritual visit place and visited the place for years and organized feasts, commemorating their ancestors with national games such as javelin and wrestling. The tomb of Ertuğrul Gazi is visited in the same way today and festivities are organized every year in Söğüt.