Set role dynamically from proc

DO 

$$

DECLARE act_dbowner varchar(100);

BEGIN

SELECT u.usename into act_dbowner FROM pg_database d

JOIN pg_user u ON (d.datdba = u.usesysid)

WHERE d.datname = (SELECT current_database());

raise notice 'DB owner: %', act_dbowner;

set role to act_dbowner; --  THIS LINE

END

$$;

-------------

ERROR:  role "act_dbowner" does not exist

CONTEXT:  SQL statement "set role to act_dbowner"

PL/pgSQL function inline_code_block line 10 at SQL statement