The judge would be required to recuse himself in that case, subject to the exception that applies when all judges with jurisdiction over the case would otherwise be disqualified.
Generally a judge must recuse in cases in which the judge as a personal interest in the case (roughly speaking the same kind of interest that would give the judge standing to participate as a party in the case), or when the judge has personal ties to the parties or their counsel that would create an appearance of impropriety.
The controlling provision of Colorado's Code of Judicial Conduct, Rule 2.11, which is typical, and its official commentary, states:
RULE 2.11. Disqualification
(A) A judge shall disqualify himself or herself in any proceeding in
which the judge's impartiality might reasonably be questioned,
including but not limited to the following circumstances:
(1) The judge has a personal bias or prejudice concerning a party or a
party's lawyer, or personal knowledge of facts that are in dispute in
(2) The judge knows that the judge, the judge's spouse or domestic
partner, or a person within the third degree of relationship to either
of them, or the spouse or domestic partner of such a person is:
(a) a party to the proceeding, or an officer, director, general
partner, managing member, or trustee of a party;
(b) acting as a lawyer in the proceeding;
(c) a person who has more than a de minimis interest that could be
substantially affected by the proceeding; or
(d) likely to be a material witness in the proceeding.
(3) The judge knows that he or she, individually or as a fiduciary, or
the judge's spouse, domestic partner, parent, child, or other member
of the judge's family residing in the judge's household, has an
economic interest in the subject matter in controversy or in a party
to the proceeding.
(4) The judge, while a judge or a judicial candidate, has made a
public statement, other than in a court proceeding, judicial decision,
or opinion, that commits or appears to commit the judge to reach a
particular result or rule in a particular way in the proceeding or
(5) The judge:
(a) served as a lawyer in the matter in controversy, or was associated
with a lawyer who participated substantially as a lawyer in the matter
during such association;
(b) served in governmental employment, and in such capacity
participated personally and substantially as a lawyer or public
official concerning the proceeding, or has publicly expressed in such
capacity an opinion concerning the merits of the particular matter in
(c) was a material witness concerning the matter; or
(d) previously presided as a judge over the matter in another court.
(B) A judge shall keep informed about the judge's personal and
fiduciary economic interests, and make a reasonable effort to keep
informed about the personal economic interests of the judge's spouse
or domestic partner and minor children residing in the judge's
(C) A judge subject to disqualification under this Rule, other than
for bias or prejudice under paragraph (A)(1), may disclose on the
record the basis of the judge's disqualification and may ask the
parties and their lawyers to consider, outside the presence of the
judge and court personnel, whether to waive disqualification. If,
following the disclosure, the parties and lawyers agree, without
participation by the judge or court personnel, that the judge should
not be disqualified, the judge may participate in the proceeding. The
agreement shall be incorporated into the record of the proceeding.
(D) In limited circumstances, the rule of necessity applies and allows
judges to hear a case in which all other judges also would have a
disqualifying interest or the case could not otherwise be heard.
 Under this Rule, a judge is disqualified whenever the judge's
impartiality might reasonably be questioned, regardless of whether any
of the specific provisions of paragraphs (A)(1) through (5) apply. The
term “recusal” is sometimes used interchangeably with the term
 A judge's obligation not to hear or decide matters in which
disqualification is required applies regardless of whether a motion to
disqualify is filed.
 The rule of necessity may override the rule of disqualification.
The rule of necessity is an exception to the principle that every
litigant is entitled to be heard by a judge who is not subject to
disqualifications which might reasonably cause the judge's
impartiality to be questioned. The rule of necessity has been invoked
for trial court and court of appeals judges where disqualifications
exist as to all members of the court and there is no other judge
available. It has been invoked as to the supreme court when all or a
majority of its members have a conflict of interest; the importance of
having the court render a decision overrides the existence of the
conflict, which might otherwise leave litigating parties in limbo.
Under the rule of necessity, a judge might be required to participate
in judicial review of a judicial salary statute, or might be the only
judge available in a matter requiring immediate judicial action, such
as a hearing on probable cause or a temporary restraining order. In
matters that require immediate action, the judge must disclose on the
record the basis for possible disqualification and make reasonable
efforts to transfer the matter to another judge as soon as
practicable. Rather than deny a party access to court, judicial
disqualification yields to the demands of necessity.
 The fact that a lawyer in a proceeding is affiliated with a law
firm with which a relative of the judge is affiliated does not itself
disqualify the judge. If, however, the judge's impartiality might
reasonably be questioned under paragraph (A), or the relative is known
by the judge to have an interest in the law firm that could be
substantially affected by the proceeding under paragraph (A)(2)(c),
the judge's disqualification is required.
 A judge should disclose on the record information that the judge
believes the parties or their lawyers might reasonably consider
relevant to a possible motion for disqualification, even if the judge
believes there is no basis for disqualification.
 “Economic interest,” as set forth in the Terminology section,
means ownership of more than a one percent legal or equitable interest
in a party, or a legal or equitable interest in a party of a fair
market value exceeding $5,000, or a relationship as a director,
advisor, or other active participant in the affairs of a party, except
that: (1) Ownership in a mutual or common investment fund that holds
securities, or of securities held in a managed fund, is not an
“economic interest” in such securities unless the judge participates
in the management of the fund;
(2) securities held by an educational, religious, charitable,
fraternal, or civic organization in which the judge or the judge's
spouse, domestic partner, parent, or child serves as a director,
officer, advisor, or other participant is not an “economic interest”
in securities held by the organization;
(3) the proprietary interest of a policy holder in a mutual insurance
company, of a depositer in a financial institution or deposits or
proprietary interests the judge may maintain as a member of a mutual
savings association or credit union, or a similar proprietary interest
is an “economic interest” in the organization only if the outcome of
the proceeding could substantially affect the value of the interest;
(4) ownership of government securities is an “economic interest” in
the issuer only if the outcome of the proceeding could substantially
affect the value of the securities.
The general rule of 2.11(A) and also 2.11(A)(2)(c) would apply in this case.