Who was the first ruler to consolidate the Slavic tribes

There was never such a person. The Slavic tribes split and worked on their own. They spread eastwards, southwards, and westwards, establishing what is nowadays known as Poland, Czech Republic, Slovakia, Ukraine, Russia, Belarus, Serbia, Bosnia, Former Yugoslavian Republic of Macedonia, Croatia, Montenegro, Slovenia, and Bulgaria.

The first ruler to consolidate the Slavic tribes was: Rurik

In the year of 862, Rurik took control of a Slavic Region called Ladoga and established the Kievan Rus, which later became the biggest Union between eastern slavic tribes during that time.

Not long after that, he established the rurik dynasty, that reign supreme within the Slavic region until the 17th century.