Robert Weiner Jr. (born February 22, 1982) is an international water polo player from the United States, who played for the University of Southern California from 2000 to 2003, and at Newport Harbor High School from 1996 to 1999.

As a High School senior he was an All-CIF player leading his team to the CIF Semi Finals and a 24–3 season record.

In 2003, Weiner was a member of the 2003 NCAA Men's Water Polo Championship team.

At USC, he majored in International Relations with a minor in Global Communications.

Also played in the Australian National Water Polo League for the UNSW Wests Magpies (2005) and in the Spanish Water Polo League for La Latina in Madrid (2003).