Archaeologically, the slavs in Modern day Bulgaria, are best researched from the sites of Popina, Garvan, Kozlodui. Also sites as Babovo, Targovishte etc. Mainly sites in North Bulgaria, and dated around the time of the early settlement of slavs (around VI c.). The ceramic complex is identified as slavic, which is represented by finds from the Penkovka culture (identified with the Antes) and finds from the Prague-Korchak culture (identified with Sclaveni).

Some of the sources that I have come across, that mention the slavs in the context of the area around Thrace, in the period around the founding of the First Bulgarian State are:

• John of Ephesus (" The accursed Slavic people conquered all of Greece, the environs of Thessaloniki, and all of Thrace. They conquered many cities and fortresses, devastated and plundered the country with fire and sword, and ruled there completely freely, as in their native country. They got rich, they have gold and silver, whole herds of horses and many weapons. They learned to wage war better than the Romans");

• Procopius of Caesarea and Maurice/Pseudo-Maurice who describe their way of life and war in the north and around the Danube and their plunders;

• Theophanes the Confessor and Nicephorus?? mention them in the context of their 'Slavic union of seven tribes' as it is generally taught and their relations with the Bulgars ("...they settled the Severi from the front gorge of Veregava to the eastern parts, and to the south and west to Avaria the other seven tribes..." "...(the Bulgars)commanded some to defend the lands bordering the Avars, and others to protect the lands adjacent to the Romans"

• Jordanes in Romana et Getica describes where the slavic tribes and Bulgars live 'past the Danube';

• Procopius mentions of a ***Khilboudios/***Chilbudius, maybe a slav??, who was a magister militum during Justinian's reign ("... In the fourth year of his reign, the emperor appointed Chilbudius as magister militum of Thrace, placed him on guard at the Istros River and ordered him to keep the local barbarians from crossing the river, as Huns, Anti and Slavs had already crossed it many times and inflicted irreparable mischief on the Romans...", alongside their raids in Thrace and Illyria, and their service in the Roman army in Italy, during the Gothic wars;

• Further about their raids we know from John Malalas, Menander (who mentions the envoy "...Mezamir, son of Idariz, brother of Kelagast" who was killed by the Avar khagan, thanks to the persuation of a Kutrigur Bulgar), Michael the Syrian, Sebeos, Theophylact Simocatta (who mentions the slavic chieftains Mužok, Peragast. And the Avaro-Slavic siege of Constantinople )

These are mainly, prior to the establishment of the Danubian Bulgar state. After that, I feel like the slavs in particular are seldom mentioned. I guess the Bulgars/Bulgar state that ruled over them, became more of an interest to the byzantine historians and the slavic tribes are included by presumption?

• Theophanes mentions: ("... [Tervel] promised with an oath that he would obey him [ Justinian] in everything and help him, received him with great honor and raised the whole army of Bulgarians and Slavs subordinated to him...") , (" In the same year [764] Pagan, the lord of Bulgaria, sent envoys to the emperor to ask to see him in person. And when he received an answer, he went down to him with his boyars. The emperor sat down, and Sabin sat with him, received them and rebuked them for their disorder and hatred of Sabin. And madeseemingly peace. And the emperor, secretly sending people to Bulgaria, captured the knyaz of the severi Slavun*, who had done many evils in Thrace. Also captured was* Kristian*, an apostate from Christianity and a chief of the* scamari [???] , whose arms and legs were cut off in the annex to the temple of St. Thomas...");
• Scriptor incertus again mentions slavs in the bulgarian army under the command of Krum, during the war with Nicephorus;
• The Süleymanköy inscription is an inscription that describes the peace deal between Omurtag and the Byzantines and part of it deals with the status of the slavic tribes on the territories of the two states and the return of prisoners ("... Chapter Two for the Slavs under the Emperor: to remain as they were when the war broke out. Chapter Three for the other Slavs who are not subordinate to the emperor in the coastal area, he will return them to their settlements...");
• The Inscription from Philippi mentions the Smolyani and The Hagiography of Gregory Dekapolites mentiones the Strymonites

Hi, Bulgarian here. I'll try to give you a short summary.

So my question is are there any traces about that Slavic people before they became Bulgars, some written history when they came there, did they have some leaders, some specific name.

From the time of the Bulgars' entry into the Balkans, to the first Bulgarian ruler with a Slavic name, there's about 150-200 years. In that time there was tenuous alliance between the two and a gradual rise in influence by Slavic chieftains. You see, Bulgars differed from other steppe nomads like the Avars and Khazars in that they gave significant rights to the Slavs they "ruled", so it didn't take long for them to start spreading into the higher echelons of the early state's nobility. Some Bulgars on the other hand saw that as a threat to their culture and opposed it, leading to a series of very bloody conflicts we know very little about. After a few slaughters of entire noble Bulgar families things quieted down.

Also fun fact, Kubrat, the ruler of Old Great Bulgaria and originator of the Dulo clan that ruled Danubian Bulgaria for centuries was a half-Slavic Christian. His sons also had Slavic wives, but they were still Tengrist.

There is written history about Croats and Serbs from that time, so probably there was some other Slavic tribes there also? Did someone wrote about them? Or they didnt have any identity before Bulgars..

They definitely had their own identity, or at least there were a bunch of various Slavic tribes/clans about the Balkans. You read about some rebellion of slavs here and there that various early Bulgar rulers had to quell, but not much more regarding why they were rebelling.