Bouvier's Law Dictionary, Revised 6th Ed (1856):

GUARDIANS, domestic relations. Guardians are divided into, guardians of the
person, in the civil law called tutors; and guardians of the estate, in the
sam law are known by the name of curators. For the distinction between them,
vide article Curatorship; 2 Kent, Com. 186 1 Bouv. Inst. n. 336, et. seq.
     2. - 1. A guardian of the person is one who has been lawfully invested
with the care of the person of an infant, whose father is dead.
     3. The guardian must be properly appointed he must be capable of
serving; he must be appointed guardian of an infant; and after his
appointment he must perform the duties imposed on him by his office.
     4. - 1st. In England, and in some of the states where the English law
has been adopted in this respect, as in Pennsylvania; Rob. Dig. 312, by
Stat. 12 Car. If. c. 24; power is given to the father to appoint a
testamentary guardian for his children, whether born or unborn. According to
Chancellor Kent, this statute has been adopted in the state of New York, and
probably throughout this country. 2 Kent, Com. 184. The statute of
Connecticut, however, is an exception; there the father cannot appoint a
testamentary guardian. 1 Swift's Dig. 48.
     5. All other kinds of guardians, to be hereafter noticed, have been
superseded in practice by guardians appointed by courts having jurisdiction
of such matters. Courts of chancery, orphans courts, and courts of a similar
character having jurisdiction of testamentary matters in the several states,
are, generally, speaking, invested with the power of appointing guardians.
     6. - 2d. The person appointed must be capable of performing the duties;
an idiot, therefore, cannot be appointed guardian.
     7. - 3d. The person over whom a guardian is appointed, must be an
infant; for after the party has attained his full age, he is entitled to all
his rights, if of sound mind, and, if not, the person appointed to take care
of him is called a committee. (q. v.) No guardian of the person can be
appointed over an infant whose father is alive, unless the latter be non
compos mentis, in which case one may be appointed, as if the latter were
dead.
     8. - 4th. After his appointment, the guardian of the person is
considered as standing in the place of the father, and of course the
relative powers and duties of guardian and ward correspond, in a great
measure, to those of parent and child; in one prominent matter they are
different. The father is entitled to the services of his child, and is bound
to support him; the guardian is not entitled to the ward's services, and is
not bound to maintain him out of his own estate.
     9. - 2. A guardian of the estate is one who has been lawfully invested
with the power of taking care and managing the estate of an infant. 1 John.
R. 561; 7 John. Ch. R. 150. His appointment is made in the same manner, as
that of a guardian of a person. It is the duty of the guardian to take
reasonable and prudent care of the estate of the ward, and manage it in the
most advantageous manner; and when the guardianship shall expire, to account
with the ward for the administration of the estate.
    10. Guardians have also been divided into guardians by nature;
guardian's by nurture; guardians in socage; testamentary guardians;
statutory guardians; and guardians ad litem.
    11. - 1. Guardian by nature, is the father, and, on his death, the
mother; this guardianship extends only to the custody of the person; 3 Bro.
C. C. 186; 1 John. Ch. R. 3; 3 Pick. R. 213; and continues till the child
shall acquire the age of twenty one years. Co. Litt. 84 a.
    12. - 2. Guardian by nurture, occurs only when the infant is without any
other guardian, and the right belongs exclusively to the parents, first to
the father, and then to the mother. It extends only to the person, and
determines, in males and females, at the age of fourteen. This species of
guardianship has become obsolete.
    13. - 3. Guardian in socage, has the custody of the infant's lands as
well as his person. The common law gave this guardianship to the next of
blood to the child to whom the inheritance could not possibly descend. This
species of guardianship has become obsolete, and does not perhaps exist in
this country; for the guardian must be a relation by blood who cannot
possibly inherit, and such a case can rarely exist. 2 Wend. 153: 15 Wend.
631; 6 Paige, 390; 7 Cowen, 36; 5 John. 66.
    14. - 4. Testamentary guardians; these are appointed under the stat. 12
Car. II., above mentioned; they supersede the claims of any other guardian,
and extend to the person, an real and personal estate of the child, and
continue till the ward arrives at full age.
    15. - 5. Guardians appointed by the courts, by virtue of statutory
authority. The distinction of guardians by nature, and by socage, appear to
have become obsolete, and have been essentially superseded in practice by
the appointment of guardians by courts of chancery, orphans' courts, probate
courts, and such other courts as have jurisdiction to, make such
appointments. Testamentary guardians might, as those of this class, be
considered as statutory guardians, inasmuch as their appointment is
authorized by a statute.
    16. - 6. Guardian ad litem, is pointed for the infant to defend him in
an action brought against him. Every court, when an infant is sued in a
civil action, has power to appoint a guardian ad litem when he has no
guardian, for as the infant cannot appoint an attorney, he would be without
assistance if such a guardian-were not appointed. The powers and duties of a
guardian ad litem are confined to the defence of the suit. F. N. B. 27; Co.
Litt. 88 b, note 16; Id. 135 b, note 1; see generally Bouv. Inst. Index, h.
t.; Coop. Inst. 445 to 455.