<page_title> List of ATP Tour Top-level tournament singles champions </page_title> <table> <cell> Grand Slam tournaments <row_header> Year </row_header> </cell> <cell> ATP Finals <row_header> Year </row_header> <row_header> Grand Slam tournaments </row_header> </cell> <cell> Masters 1000 Series <row_header> Year </row_header> <row_header> Grand Slam tournaments </row_header> <row_header> ATP Finals </row_header> </cell> <cell> Olympics <row_header> Year </row_header> <row_header> Grand Slam tournaments </row_header> <row_header> ATP Finals </row_header> <row_header> Masters 1000 Series </row_header> </cell> <cell> 1990 <col_header> Year </col_header> <col_header> AO </col_header> </cell> </table>
Grand Slam tournaments, the ATP Finals, the Masters series and the Olympics are four tiers since the introduction of the ATP Tour in 1990.