Final answer:
Peter I, or Peter the Great, was the Tsar who abolished the boyar seniority system in Moscow, centralizing power and modernizing Russia.
Step-by-step explanation:
The Tsar who got rid of the boyar seniority system in Moscow was Peter I, also known as Peter the Great. His reign brought about significant reforms that aimed at modernizing Russia, including a change in the old Russian government system where power was distributed among the boyars, the highest-ranking members of the Russian nobility. Peter I's efforts led to the centralization of power and the establishment of a more autocratic government, which laid the foundations for the eventual transformation of Russia into a major European power.